CN113683089B - Layered porous biochar and preparation method and application thereof - Google Patents
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- 238000000034 method Methods 0.000 claims abstract description 24
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Classifications
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- C—CHEMISTRY; METALLURGY
- C01—INORGANIC CHEMISTRY
- C01B—NON-METALLIC ELEMENTS; COMPOUNDS THEREOF; METALLOIDS OR COMPOUNDS THEREOF NOT COVERED BY SUBCLASS C01C
- C01B32/00—Carbon; Compounds thereof
- C01B32/30—Active carbon
- C01B32/312—Preparation
- C01B32/342—Preparation characterised by non-gaseous activating agents
- C01B32/348—Metallic compounds
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
- B01J—CHEMICAL OR PHYSICAL PROCESSES, e.g. CATALYSIS OR COLLOID CHEMISTRY; THEIR RELEVANT APPARATUS
- B01J20/00—Solid sorbent compositions or filter aid compositions; Sorbents for chromatography; Processes for preparing, regenerating or reactivating thereof
- B01J20/02—Solid sorbent compositions or filter aid compositions; Sorbents for chromatography; Processes for preparing, regenerating or reactivating thereof comprising inorganic material
- B01J20/20—Solid sorbent compositions or filter aid compositions; Sorbents for chromatography; Processes for preparing, regenerating or reactivating thereof comprising inorganic material comprising free carbon; comprising carbon obtained by carbonising processes
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
- B01J—CHEMICAL OR PHYSICAL PROCESSES, e.g. CATALYSIS OR COLLOID CHEMISTRY; THEIR RELEVANT APPARATUS
- B01J20/00—Solid sorbent compositions or filter aid compositions; Sorbents for chromatography; Processes for preparing, regenerating or reactivating thereof
- B01J20/28—Solid sorbent compositions or filter aid compositions; Sorbents for chromatography; Processes for preparing, regenerating or reactivating thereof characterised by their form or physical properties
- B01J20/28054—Solid sorbent compositions or filter aid compositions; Sorbents for chromatography; Processes for preparing, regenerating or reactivating thereof characterised by their form or physical properties characterised by their surface properties or porosity
- B01J20/28057—Surface area, e.g. B.E.T specific surface area
- B01J20/28061—Surface area, e.g. B.E.T specific surface area being in the range 100-500 m2/g
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
- B01J—CHEMICAL OR PHYSICAL PROCESSES, e.g. CATALYSIS OR COLLOID CHEMISTRY; THEIR RELEVANT APPARATUS
- B01J20/00—Solid sorbent compositions or filter aid compositions; Sorbents for chromatography; Processes for preparing, regenerating or reactivating thereof
- B01J20/28—Solid sorbent compositions or filter aid compositions; Sorbents for chromatography; Processes for preparing, regenerating or reactivating thereof characterised by their form or physical properties
- B01J20/28054—Solid sorbent compositions or filter aid compositions; Sorbents for chromatography; Processes for preparing, regenerating or reactivating thereof characterised by their form or physical properties characterised by their surface properties or porosity
- B01J20/28078—Pore diameter
- B01J20/2808—Pore diameter being less than 2 nm, i.e. micropores or nanopores
-
- C—CHEMISTRY; METALLURGY
- C01—INORGANIC CHEMISTRY
- C01B—NON-METALLIC ELEMENTS; COMPOUNDS THEREOF; METALLOIDS OR COMPOUNDS THEREOF NOT COVERED BY SUBCLASS C01C
- C01B32/00—Carbon; Compounds thereof
- C01B32/30—Active carbon
- C01B32/312—Preparation
- C01B32/318—Preparation characterised by the starting materials
- C01B32/324—Preparation characterised by the starting materials from waste materials, e.g. tyres or spent sulfite pulp liquor
-
- C—CHEMISTRY; METALLURGY
- C02—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
- C02F—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
- C02F1/00—Treatment of water, waste water, or sewage
- C02F1/28—Treatment of water, waste water, or sewage by sorption
- C02F1/283—Treatment of water, waste water, or sewage by sorption using coal, charred products, or inorganic mixtures containing them
-
- C—CHEMISTRY; METALLURGY
- C02—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
- C02F—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
- C02F1/00—Treatment of water, waste water, or sewage
- C02F1/70—Treatment of water, waste water, or sewage by reduction
-
- C—CHEMISTRY; METALLURGY
- C02—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
- C02F—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
- C02F2101/00—Nature of the contaminant
- C02F2101/10—Inorganic compounds
- C02F2101/20—Heavy metals or heavy metal compounds
- C02F2101/22—Chromium or chromium compounds, e.g. chromates
-
- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
- Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
- Y02E50/00—Technologies for the production of fuel of non-fossil origin
- Y02E50/10—Biofuels, e.g. bio-diesel
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- Chemical & Material Sciences (AREA)
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- Engineering & Computer Science (AREA)
- Analytical Chemistry (AREA)
- Environmental & Geological Engineering (AREA)
- Inorganic Chemistry (AREA)
- Chemical Kinetics & Catalysis (AREA)
- Life Sciences & Earth Sciences (AREA)
- Hydrology & Water Resources (AREA)
- Water Supply & Treatment (AREA)
- Materials Engineering (AREA)
- Nanotechnology (AREA)
- Carbon And Carbon Compounds (AREA)
Abstract
The invention discloses a layered porous biochar and a preparation method and application thereof, wherein the preparation method of the layered porous biochar comprises the following steps: (1) biomass raw material preparation; (2) delignification treatment; (3) carbonizing lignin-removed wood chips; (4), activation: and (3) performing KOH activation on carbonized delignified wood chips, and performing pyrolysis under inert gas to obtain layered porous biochar. The preparation method provided by the invention is simple and feasible, expensive equipment is not needed, the raw material source is wide, the cost is low, the regeneration is realized, the heavy metal removing capability is obvious, and the method can be widely applied to other biomass materials.
Description
Technical Field
The invention belongs to the technical field of biochar preparation and heavy metal removal, and particularly relates to layered porous biochar, a preparation method thereof and application thereof in heavy metal removal.
Background
Along with the development of industrial technology, chromium and its compounds are widely used in the industries of paint, pigment, metallurgy, leather, electroplating, textile and the like. However, these industries produce large amounts of chromium-containing wastewater, which is mainly in the form of Cr (III) and Cr (VI), wherein Cr (VI) is a persistent contaminant, and Cr is 2 O 7 2- And HCrO 4 - The form of the water-based ecological agent is in water, has the characteristics of high fluidity and high toxicity, can freely migrate into an aquatic ecological system and organisms, and can cause huge damage to the ecological system and threaten the growth and reproduction of the aquatic organisms. And chromates can irritate and erode human skin, inhibit cellular metabolic processes, and cause cancer,Inducing gene mutation, etc. Therefore, the treatment of the chromium-containing wastewater is always an important research topic in the field of water environment protection. In order to solve this problem, researchers have studied the removal of Cr (VI) from sewage by chemical precipitation, membrane filtration, ion exchange, solvent extraction, adsorption, and the like. Among the many adsorbents currently in use, carbon-based adsorbents are considered good adsorbents, which have a high surface area, a controlled particle size, good adsorption and low production costs. The carbon-based adsorbent takes biomass as a raw material and prepares the high-performance adsorbent in a carbonization-activation mode, but the currently used adsorbent has poor adsorption effect, single adsorption mechanism or prepares the carbon-based adsorbent by using an expensive raw material (glucose) for pursuing high adsorption effect, and the adsorbents have certain limitations in practical application.
Content of study
The invention aims to overcome the defects of low adsorption performance and incomplete biomass utilization in the existing biochar adsorption technology. The biochar with excellent adsorption performance is provided, the preparation method is simple to operate, the cost is low, and the pollutant adsorption efficiency is high. The invention removes lignin which is the main component of the cell wall of the wood chips of the biomass material, loosens the wood structure, increases the surface area, is beneficial to the later activation, prepares the biochar material, and lays a certain foundation for practical application through a batch Cr (VI) adsorption experiment.
A method for preparing layered porous biochar, comprising the following steps:
(1) Raw material preparation:
the biomass raw material adopts forestry processing wood chips;
(2) And (3) lignin removal treatment:
removing lignin from the wood chips;
(3) Carbonizing lignin-removed wood chips:
pyrolyzing the delignified wood chips under inert gas to obtain carbonized delignified wood chips;
(4) And (3) activating:
and (3) carbonizing the lignin-removed wood chips to perform alkali activation, and then performing pyrolysis under inert gas to obtain layered porous biochar.
Further, in the step (1), the wood chips are sieved by a 60-mesh sieve, washed by deionized water and ethanol and then dried; wood dust from poplar is preferred. And (3) further, sieving the wood dust in the step (1) by a 60-mesh sieve, removing large-particle dust and other crushed impurities in the wood dust, ultrasonically cleaning the wood dust by absolute ethyl alcohol and deionized water for a plurality of times, and drying the wood dust in an oven at 60 ℃ for 24 hours.
Further, the specific process of the delignification treatment in the step (2): with NaOH and Na 2 SO 3 Removing lignin by completely soaking wood chips in the mixed solution, boiling, pouring out waste liquid, boiling and washing with water for multiple times until the washed solution is colorless, and using H 2 O 2 Soaking lignin-removed wood chips in the solution, adjusting the pH of the solution to be alkaline during soaking, finally washing the wood chips with water until the solution is neutral, and drying to obtain the lignin-removed wood chips.
Further, in the step (2), 0.1-2 mmol/L NaOH and 0.1-2 mmol/L Na are adopted 2 SO 3 The volume ratio of the two is 0.5: 1-2: 1, preferably 1 to 1.5mmol/L NaOH and not more than 0.5mmol/L Na 2 SO 3 Preferably, the volume ratio of the two is 1:1.
further, naOH and Na are added in the step (2) 2 SO 3 The reaction is carried out at 90-110 ℃, and the waste liquid is poured out after the water bath kettle is boiled for 1-10 hours.
Further, the step (2) is carried out by using 2 to 5%H 2 O 2 Soaking the wood chips with lignin removed in the solution for 1-3 h, and adding ammonia water to adjust the pH of the solution to be alkaline during soaking, wherein the pH is preferably 9-11; finally, the wood chips are washed by deionized water until the solution is neutral, and the lignin-removed wood chips are obtained by drying.
Further, the lignin-removed wood chips in the step (3) are placed under inert gas for pyrolysis, a certain heating rate is maintained, the pyrolysis temperature is 650-750 ℃, and the pyrolysis time is 1-3 hours; preferably the inert gas is N 2 The temperature rising rate is 2-10 ℃/min.
Further, in the step (4), KOH is adopted for activation; mixing KOH and the prepared carbonized delignified wood chips, grinding uniformly, adding water, stirring for dissolving, and drying; (the purpose of adding water is to dissolve KOH)
Further, the pyrolysis temperature in the step (4) is 650-750 ℃ and the pyrolysis time is 1-3 hours; preferably the inert gas is N 2 The temperature rising rate is 2-10 ℃/min; preferably, in the step (4), the mass ratio of KOH/carbonized delignified wood chips=3: 1 to 5:1.
after pyrolysis and cooling, thoroughly washing the mixture for several times by using HCl to remove soluble inorganic salts, washing the mixture by using distilled water until the pH value reaches neutrality, and drying the mixture to obtain layered porous biochar; preferably in a vacuum oven at 100 c for 12 hours.
The second object of the invention is to provide the layered porous biochar prepared by the method.
A third object of the present invention is to provide an application of the layered porous biochar prepared by the above method for removing contaminants; comprising the following steps: heavy metals, antibiotics, pesticide residues, especially hexavalent chromium.
In the invention, an adsorption experiment is carried out by taking 30mL of solution with the chromium ion concentration of 100mg/L as an example, and the addition amount of the layered porous biochar is 0.005-0.02 g.
Further, the pH at the time of adsorption is 1 to 8, preferably pH 2; the temperature ranges from 20 ℃ to 50 ℃, preferably 25 ℃, and the adsorption time is at least 12 hours.
Further, HCl and NaOH are used for adjusting the pH value of the heavy metal solution; after adsorption, the solution was filtered through a 0.45 μm filter.
The invention adopts Cr (VI) batch adsorption experiment
Batch adsorption measurements of Cr (VI) at different concentrations were performed in conical flasks. The hexavalent chromium concentrations were calibrated using potassium dichromate. Taking Cr (VI) solution with a certain concentration, adding a certain amount of adsorbent, and adjusting the pH value of the solution by using HCl and NaOH. After adsorption, the resultant was filtered through a 0.45 μm filter membrane, and the Cr (VI) concentration was measured by an ultraviolet spectrophotometer. In the adsorption experiment, the influence of different adsorbent types, initial concentration of adsorption solution, pH and the like on Cr (VI) adsorption is examined, and the adsorption mechanism is explored.
The beneficial effects of the invention are as follows:
1. the preparation method of the layered porous biochar material has simple process and good layered structure, and after delignification treatment, through SEM characterization, the original compact poplar structure is changed into a fiber layer with regular arrangement, and the surface area is increased from 57.3 to 236.4m 2 And/g. The adsorption amount was changed from 18.21mg/g of raw poplar charcoal to 63.42mg/g after delignification and reached 288.90mg/g after further activation, compared to 154.5mg/g for activated poplar charcoal without delignification.
2、N 2 Adsorption-desorption experiments show that the isotherm of the layered porous biochar prepared by the invention is a mixture of type I and type IV, and has higher absorptivity under lower relative pressure, which indicates that abundant micropores are generated; the hysteresis loop between the adsorption and desorption isotherms is more evident, indicating mesoporous development. In addition, based on pore size distribution diagrams of the BJH method and the DFT method, compared with the original poplar wood chip carbon, delignification and KOH activation can improve the medium and micropore volumes of the delignified poplar wood chip carbon and the layered porous biochar, so that the specific surface area is obviously increased.
3. The layered porous biochar material prepared by the invention has the advantages that the optimal adsorption pH value is 2 through Cr (VI) adsorption experiments with different concentrations and different pH values, the adsorption rate is faster at low concentration, the adsorption equilibrium time is 12h, and when the concentration of Cr (VI) exceeds 60mg/L, the removal rate is reduced, and the adsorption equilibrium time is prolonged.
4. The layered porous biochar material prepared by the invention has zero charge point (pH value PZC ) Is 1.7, so when the pH is<pH PZC When it is protonated, the functional groups on the layered porous biochar, thereby rendering the negatively charged HCrO 4 - And Cr (V) 2 O 7 2- Is adsorbed onto the layered porous biochar by electrostatic attraction. When the solution pH is increased from 1.7 to 8.0, the absorption of Cr (VI) is significantly reduced due to the electrostatic repulsion of the anionic Cr (VI) by the negatively charged layered porous biochar.
5. The layered porous biochar material prepared by the invention has rich functional groups on the surface through a later batch chromium adsorption experiment, and can reduce Cr (VI) into low-toxicity Cr (III) and fix the Cr (VI) on the surface of activated delignified charcoal.
6. The layered porous biochar material prepared by the invention is subjected to dynamic model and isothermal line model fitting, the process of adsorbing Cr (VI) accords with the second-level dynamics, the adsorption process is proved to be chemical reaction leading, and the isothermal fitting accords with the Langmuir model, so that the adsorption process is proved to be endothermic.
7. According to the energy spectrum analysis of the layered porous biochar prepared by the invention after Cr (VI) is adsorbed, the element map after the adsorption experiment shows that C, O, cr elements are uniformly distributed on the surface of the layered porous biochar. EDS spectrum shows that Cr with the mass ratio of 45.14% and the atomic ratio of 17.81% exists in different valence states, cr (III) and Cr (VI) exist, and further shows that the layered porous biochar has good adsorption performance, and also shows that some Cr (VI) fixes chromium ions on the surface of the layered porous biochar through reduction reaction with functional groups on the surface of the layered porous biochar.
8. As can be seen from the X-ray photoelectron spectrum after Cr (VI) is adsorbed by the layered porous biochar prepared by the invention, the characteristic difference of chemical components of the layered porous biochar before and after Cr (VI) is adsorbed is researched by the X-ray photoelectron spectrum, and the adsorption mechanism of the layered porous biochar on chromium is revealed. The x-ray photoelectron spectra showed that the characteristic spin orbit peaks at 576.38, 580.93 and 586.36eV were Cr (III) and the characteristic spin orbit peaks at 588.86 and 577.79eV were Cr (VI), indicating partial reduction of the original Cr (VI) to lower Cr (III). Furthermore, in c=o (530.84 eV), O-c=o (531.76 eV) and C-O (532.98 eV), the spin-orbit peaks of O1s after Cr adsorption undergo a red shift of binding energy at 529.60, 531.00 and 532.23eV, respectively (fig. 9C-d). This phenomenon may be caused by complex compounds formed by the interaction (e.g., ion exchange) and complexation of lone pair electrons of oxygen-containing groups (i.e., carboxyl and hydroxyl groups) with Cr (VI).
9. The preparation method provided by the invention is simple and feasible, expensive equipment is not needed, the raw material source is wide, the cost is low, the regeneration is realized, and the method can be widely applied to other biomass materials.
Drawings
FIG. 1 shows Zeta potential diagrams of (a) the adsorption amount of Cr (VI) by the layered porous biochar at different pH values and (b) the layered porous biochar at different pH values in example 1.
FIG. 2 is a scanning electron microscope image of the sample in example 2: (a) is a poplar charcoal scanning electron microscope image; (b) scanning electron microscopy of delignified poplar charcoal; (c) the layered porous biochar of the present invention; (d) adsorption comparison graph of four kinds of biochar to Cr (VI).
FIG. 3 is a graph showing nitrogen adsorption-desorption curves of poplar charcoal, delignified poplar charcoal and layered porous biochar of the present invention in example 2.
FIG. 4 is a graph showing pore size distribution of poplar charcoal, delignified poplar charcoal and layered porous biochar of the present invention according to BJH method (FIG. 4 a) and DFT method (FIG. 4 b) in example 2.
FIG. 5 shows the effect of the layered porous biochar on the adsorption of different initial concentrations of Cr (VI) in example 3, (a) the adsorption amount of the layered porous biochar on the adsorption of different initial concentrations of Cr (VI), and (b) the removal rate of the adsorption of different initial concentrations of Cr (VI).
FIG. 6 is a fitted graph of isothermal models of the adsorption of Cr (VI) by layered porous biochar in example 4.
FIG. 7 is a fitted graph of a kinetic model of the adsorption of Cr (VI) by the layered porous biochar in example 5.
FIG. 8 is a graph showing the uniform distribution of the elements C, O, cr on the surface of the layered porous biochar element map after the adsorption test (a-d) by energy spectrum analysis after Cr (VI) is adsorbed by the layered porous biochar in example 6; (e) EDS maps.
FIG. 9 is a graph showing the total measurement scan of XPS spectra after (a) adsorption of the layered porous biochar of example 6 with X-ray photoelectron spectroscopy before and after Cr (VI) adsorption; (b) high resolution XPS spectroscopy of Cr 2p after adsorption; (c) O1s prior to adsorption; (d) O1s after adsorption.
In the above figures:
delignified poplar charcoal, i.e., delignified unactivated poplar charcoal;
activated charcoal, i.e. activated poplar charcoal without delignification
Lignin is lignin.
Detailed Description
The following examples are intended to further illustrate the invention, but not to limit it.
Example 1:
1. raw material treatment:
the waste poplar scraps are firstly screened by 60 meshes, redundant soil and other impurities are removed, the surfaces of the poplar scraps are washed by ethanol to remove waxes and other oily components, and the poplar scraps are washed by deionized water for a plurality of times and are dried for 24 hours at 60 ℃ in a blast drying box.
2. Removing lignin from raw materials:
with 1.25mmol/L NaOH and 0.2mmol/L Na 2 SO 3 The mixed solution (volume ratio is 1:1) of the mixture is completely immersed in the poplar wood chips, then the water bath kettle is boiled for 5 hours, the waste liquid is poured out, the solution is boiled and washed for a plurality of times by deionized water until the washed solution is colorless, and 3%H is used 2 O 2 Soaking the lignin-removed poplar wood chips in the solution for 2 hours, adding ammonia water to adjust the pH of the solution to 9 during soaking, thoroughly cleaning the poplar wood chips to be neutral after the completion, and freeze-drying to obtain the lignin-removed poplar wood chips.
3. Carbonization of delignified wood:
and (3) placing the delignified poplar wood chips into a tubular furnace for pyrolysis under inert gas, maintaining a certain heating rate, and obtaining carbonized delignified wood chips at the pyrolysis temperature of 700 ℃ for 2 hours.
4. Activating KOH:
the carbonized delignified wood chips are subjected to KOH activation (KOH: carbon=4:1), KOH and the prepared carbonized delignified wood are ground uniformly in a mortar, then added with water for dissolution and drying, placed in a tube furnace for pyrolysis under inert gas, the pyrolysis temperature is kept at 700 ℃, the pyrolysis time is 2 hours, after cooling, the carbonized delignified wood chips are thoroughly washed with 1mol/LHCl for several times, soluble inorganic salts are removed, and then distilled water is used for washing until the pH value reaches neutrality. And drying in a vacuum oven at 100 ℃ for 12 hours to obtain the layered porous biochar.
5. Zeta potential measurement of layered porous biochar
Dispersing 0.01g of layered porous biochar in 100mL of water, dropwise adding one drop of ethanol, performing ultrasonic treatment for 30min, adjusting the pH value of the solution to be 1-8, and measuring the Zeta potential of the layered porous biochar by utilizing a nano-particle size and Zeta potential analyzer.
6. Determination of optimal adsorption pH by Cr (VI) batch adsorption experiments
The layered porous biochar prepared as described above was used as an adsorbent, and batch adsorption measurements of Cr (VI) at different pH were performed in a conical flask. The concentration of Cr (VI) solution is 100mg/L, then 30mL of Cr (VI) solution is taken in a 50mL conical flask, the dosage of the adsorbent is 0.01g, and the pH value of the adsorption environment is regulated to be 1-8 by HCl and NaOH, and the temperature is 25 ℃. After adsorption, the solution was filtered through a 0.45 μm filter, and the Cr (VI) concentration was measured by an ultraviolet spectrophotometer to determine the optimum pH for adsorption.
Example 2:
1. removing lignin from raw materials:
the raw materials are forestry processing waste poplar wood dust (60 meshes) and 1.25mmol/L NaOH and 0.2mmol/L Na 2 SO 3 The mixed solution with the volume ratio of 1:1 is completely soaked in the poplar wood chips, then the water bath kettle is boiled for 5 hours, the waste liquid is poured out, and the mixture is boiled and washed for multiple times by deionized water, and 3 percent H is used 2 O 2 Soaking the lignin-removed poplar wood chips in the solution for 2 hours, adding ammonia water to adjust the pH of the solution to 9 during soaking, thoroughly cleaning the poplar wood chips to be neutral after the completion, and freeze-drying to obtain the lignin-removed poplar wood chips.
2. Carbonization of delignified wood:
the delignified poplar wood chips are placed in a tubular furnace to be pyrolyzed under inert gas, a certain heating rate is maintained, the pyrolysis temperature is 700 ℃, and the pyrolysis time is 2 hours, so that carbonized delignified wood is obtained.
3. Activating KOH:
KOH activation (KOH: carbon=4:1) is carried out on carbonized delignified wood, KOH and the prepared carbonized delignified wood are ground uniformly in a mortar, then water is added for dissolution and drying, the mixture is placed in a tube furnace for pyrolysis under inert gas, a certain heating rate is maintained, the pyrolysis temperature is 700 ℃, the pyrolysis time is 2 hours, after cooling, the mixture is thoroughly washed with 1mol/LHCl for several times, soluble inorganic salts are removed, and then distilled water is used for washing until the pH value reaches neutrality. And drying in a vacuum oven at 100 ℃ for 12 hours to obtain the layered porous biochar.
4. Cr (VI) batch adsorption experiment is used for determining the adsorption quantity of four materials
Four carbon materials are adopted: poplar charcoal (the above preparation process did not undergo delignification and activation, the pyrolysis carbonization process in step 3 was directly conducted after crushing and sieving), delignified poplar charcoal (the above preparation process did not undergo carbonization in step 2 and activation in step 3, the pyrolysis carbonization in step 3 was directly conducted after delignification), activated charcoal (the above preparation process did not undergo delignification in step 1, the activation in step 3 and pyrolysis carbonization process were directly conducted after crushing and sieving), and the layered porous biochar prepared in this example were subjected to batch adsorption measurement of Cr (VI) by four materials in a conical flask. The initial concentration of the 30mLCr (VI) solution was set at 100mg/L, the amount of adsorbent was 0.01g, the pH of the adsorption environment was 2, and the temperature was 25 ℃. After adsorption, the resultant was filtered through a 0.45 μm filter, and the Cr (VI) concentration was measured by an ultraviolet spectrophotometer to determine the adsorption amounts of the four materials.
In addition, nitrogen adsorption-desorption curve tests of poplar charcoal, delignified poplar charcoal and layered porous biochar prepared in this example, and pore size tests based on BJH method and DFT method were also performed.
Example 3:
1. removing lignin from raw materials:
the raw materials are forestry processing waste poplar wood dust (60 meshes) and 1.25mmol/L NaOH and 0.2mmol/L Na 2 SO 3 The mixed solution (volume ratio is 1:1) of the mixture is completely immersed in the poplar wood chips, then the water bath kettle is boiled for 5 hours, the waste liquid is poured out, and the mixture is boiled and washed for multiple times by deionized water, and 3 percent of H is used 2 O 2 Soaking the lignin-removed poplar wood chips in the solution for 2 hours, adding ammonia water to adjust the pH of the solution to 9 during soaking, thoroughly cleaning the poplar wood chips to be neutral after the completion of the soaking, and freeze-drying to obtain the lignin-removed poplar wood chips.
2. Carbonization of delignified wood:
the delignified poplar wood chips are placed in a tubular furnace to be pyrolyzed under inert gas, a certain heating rate is maintained, the pyrolysis temperature is 700 ℃, and the pyrolysis time is 2 hours, so that carbonized delignified wood is obtained.
3. Activating KOH:
KOH activation (KOH: carbon=4:1) is carried out on carbonized delignified wood, KOH and the prepared carbonized delignified wood are ground uniformly in a mortar, then water is added for dissolution and drying, the mixture is placed in a tube furnace for pyrolysis under inert gas, a certain heating rate is maintained, the pyrolysis temperature is 700 ℃, the pyrolysis time is 2 hours, after cooling, the mixture is thoroughly washed with 1mol/LHCl for several times, soluble inorganic salts are removed, and then distilled water is used for washing until the pH value reaches neutrality. And drying in a vacuum oven at 100 ℃ for 12 hours to obtain the layered porous biochar.
4. Cr (VI) batch adsorption experiment to test the adsorption amount of different chromium initial concentrations
The layered porous biochar prepared by the method is used as an adsorbent, and batch adsorption measurement of Cr (VI) with different concentrations is carried out in a conical flask. The hexavalent chromium concentrations were calibrated using potassium dichromate. The concentration of 30mL of Cr (VI) solution was set at 40, 60, 100, 150 and 200mg/L, 0.01g of adsorbent was added, the pH of the adsorption environment was 2, the temperature was 25℃and the pH of the solution was adjusted with HCl and NaOH. After adsorption, the resultant was filtered through a 0.45 μm filter membrane, and the Cr (VI) concentration was measured by an ultraviolet spectrophotometer.
Example 4:
1. removing lignin from raw materials:
the raw materials are forestry processing waste poplar wood dust (60 meshes) and 1.25mmol/L NaOH and 0.2mmol/L Na 2 SO 3 The mixed solution with the volume ratio of 1:1 is completely soaked in the poplar wood chips, then the water bath kettle is boiled for 5 hours, the waste liquid is poured out, and the mixture is boiled and washed for multiple times by deionized water, and 3%H is used 2 O 2 Soaking the lignin-removed poplar wood chips in the solution for 2 hours, adding ammonia water to adjust the pH of the solution to 9 during soaking, thoroughly cleaning the poplar wood chips to be neutral after the completion of the soaking, and freeze-drying to obtain the lignin-removed poplar wood chips.
2. Carbonization of delignified wood:
the delignified poplar wood chips are placed in a tubular furnace to be pyrolyzed under inert gas, a certain heating rate is maintained, the pyrolysis temperature is 700 ℃, and the pyrolysis time is 2 hours, so that carbonized delignified wood is obtained.
3. Activating KOH:
KOH activation (KOH: carbon=4:1) is carried out on carbonized delignified wood, KOH and the prepared carbonized delignified wood are ground uniformly in a mortar, then water is added for dissolution and drying, the mixture is placed in a tube furnace for pyrolysis under inert gas, a certain heating rate is maintained, the pyrolysis temperature is 700 ℃, the pyrolysis time is 2 hours, after cooling, the mixture is thoroughly washed with 1mol/LHCl for several times, soluble inorganic salts are removed, and then distilled water is used for washing until the pH value reaches neutrality. And drying in a vacuum oven at 100 ℃ for 12 hours to obtain the layered porous biochar.
4. Cr (VI) batch adsorption experiment is used for determining adsorption quantity at different temperatures and isothermal adsorption simulation
Batch adsorption measurements of Cr (VI) at different temperatures were performed in conical flasks. The hexavalent chromium concentrations were calibrated using potassium dichromate. The concentration of 30mL of Cr (VI) solution was 100mg/L, the amount of adsorbent was 0.01g, the pH of the adsorption environment was 2, and the temperatures were 25 ℃ (298K), 35 ℃ (308K) and 45 ℃ (318K). The pH of the solution was adjusted with HCl and NaOH. After adsorption, the resultant was filtered through a 0.45 μm filter membrane, and the Cr (VI) concentration was measured by an ultraviolet spectrophotometer. The resulting data were fitted using the Freundlich and Langmuir models.
Example 5:
1. removing lignin from raw materials:
the raw materials are forestry processing waste poplar wood dust (60 meshes) and 1.25mmol/L NaOH and 0.2mmol/L Na 2 SO 3 The mixed solution with the volume ratio of 1:1 is completely soaked in the poplar wood chips, then the water bath kettle is boiled for 5 hours, the waste liquid is poured out, and the mixture is boiled and washed for multiple times by deionized water, and 3%H is used 2 O 2 Soaking the lignin-removed poplar wood chips in the solution for 2 hours, adding ammonia water to adjust the pH of the solution to 9 during soaking, thoroughly cleaning the poplar wood chips to be neutral after the completion, and freeze-drying to obtain the lignin-removed poplar wood chips.
2. Carbonization of delignified wood:
the delignified poplar wood chips are placed in a tubular furnace to be pyrolyzed under inert gas, a certain heating rate is maintained, the pyrolysis temperature is 700 ℃, and the pyrolysis time is 2 hours, so that carbonized delignified wood is obtained.
3. Activating KOH:
KOH activation (KOH: carbon=4:1) is carried out on carbonized delignified wood, KOH and the prepared carbonized delignified wood are ground uniformly in a mortar, then water is added for dissolution and drying, the mixture is placed in a tube furnace for pyrolysis under inert gas, a certain heating rate is maintained, the pyrolysis temperature is 700 ℃, the pyrolysis time is 2 hours, after cooling, the mixture is thoroughly washed with 1mol/LHCl for several times, soluble inorganic salts are removed, and then distilled water is used for washing until the pH value reaches neutrality. And drying in a vacuum oven at 100 ℃ for 12 hours to obtain the layered porous biochar.
4. Cr (VI) batch adsorption experiment determines adsorption kinetics of layered porous biochar adsorption
Batch adsorption measurements of Cr (VI) were performed in conical flasks. The hexavalent chromium concentrations were calibrated using potassium dichromate. The concentration of the Cr (VI) solution was 60mg/L, the volume was 30mL, the amount of the adsorbent was 0.01g, the pH of the adsorption environment was 2, and the temperature was 25 ℃. The Cr (VI) concentrations were measured with an ultraviolet spectrophotometer after the adsorption amounts of 0.5h, 1h, 2h, 3h, 5h, 8h, 12h, 18h and 24h, respectively. And fitting and analyzing the obtained data by adopting pseudo first-order dynamics and pseudo second-order dynamics.
Example 6:
1. removing lignin from raw materials:
the raw materials are forestry processing waste poplar wood dust (60 meshes) and 1.25mmol/L NaOH and 0.2mmol/L Na 2 SO 3 The mixed solution of (2) is completely immersed in the poplar wood chips, then the water bath kettle is boiled for 5 hours, the waste liquid is poured out, deionized water is used for boiling and washing for multiple times, and 3 percent of H is used 2 O 2 Soaking the lignin-removed poplar wood chips in the solution for 2 hours, adding ammonia water to adjust the pH of the solution to 9 during soaking, thoroughly cleaning the poplar wood chips to be neutral after the completion, and freeze-drying to obtain the lignin-removed poplar wood chips.
2. Carbonization of delignified wood:
the delignified poplar wood chips are placed in a tubular furnace to be pyrolyzed under inert gas, a certain heating rate is maintained, the pyrolysis temperature is 700 ℃, and the pyrolysis time is 2 hours, so that carbonized delignified wood is obtained.
3. Activating KOH:
KOH activation (KOH: carbon=4:1) is carried out on carbonized delignified wood, KOH and the prepared carbonized delignified wood are ground uniformly in a mortar, then water is added for dissolution and drying, the mixture is placed in a tube furnace for pyrolysis under inert gas, a certain heating rate is maintained, the pyrolysis temperature is 700 ℃, the pyrolysis time is 2 hours, after cooling, the mixture is thoroughly washed with 1mol/LHCl for several times, soluble inorganic salts are removed, and then distilled water is used for washing until the pH value reaches neutrality. And drying in a vacuum oven at 100 ℃ for 12 hours to obtain the layered porous biochar.
4. Cr (VI) batch adsorption experiment tests adsorption mechanism after adsorption
The layered porous biochar prepared as described above was used as an adsorbent, and batch adsorption measurement of Cr (VI) was performed in a conical flask. The concentration of hexavalent chromium was calibrated using potassium dichromate. 30mL of a 100mg/L Cr (VI) solution was taken, 0.01g of an adsorbent was added thereto, the pH of the adsorption environment was 2, the temperature was 25℃and the pH of the solution was adjusted with HCl and NaOH. After adsorption, the resultant was filtered through a 0.45 μm filter membrane, and the Cr (VI) concentration was measured by an ultraviolet spectrophotometer. And collecting the adsorbent after adsorption, and carrying out scanning electron microscope-energy spectrum and X-ray photoelectron energy spectrum analysis.
Experimental results:
fig. 1 shows the Zeta potential of the layered porous biochar of example 1 (a) for Cr (vi) at different pH and (b) at different pH, and shows that the adsorption amount is highest when ph=2. The pH-dependent environment of the Cr (VI) adsorption process is illustrated. In practical applications, care should be taken to adjust the adsorption environment to be acidic (pH 1-3) to ensure a higher adsorption capacity. From graph b, it can be seen that the zero charge point (pH PZC ) Is 1.7, which illustrates that the layered porous biochar is positively charged at a pH < 1.7. The layered porous biochar exhibits electronegativity at a pH > 1.7. So when pH is<pH PZC When it is protonated, it activates the functional groups on delignified poplar charcoal, thereby rendering the negatively charged HCrO 4 - And Cr (V) 2 O 7 2- Is adsorbed onto the layered porous biochar by electrostatic attraction. So when the pH of the solution is increased from 1.7By 8.0, the absorption of Cr (VI) is significantly reduced due to the electrostatic repulsion of the negative charge of the layered porous biochar to the anion Cr (VI).
FIG. 2 is a scanning electron microscope image of the sample in example 2: (a) is a poplar charcoal scanning electron microscope image; (b) scanning electron microscopy of delignified poplar charcoal; (c) layered porous biochar; (d) adsorption comparison graph of four kinds of biochar to Cr (VI). From the figure, the natural poplar wood chips have compact and thicker cell wall structure (figure 1 a), and after delignification carbonization, the delignified poplar wood charcoal has a typical multi-layer structure (figure 2 b) due to the retained cellulose microfibers arranged in the layers, which is beneficial to improving the specific surface area and expanding the porosity, so that good adsorption performance is obtained. Simple KOH activation yields layered porous biochar with a multi-layer structure (fig. 2 c). In fig. 2d, the adsorption of poplar charcoal prepared from untreated wood was very low. The surface area increases after delignification, the adsorption capacity increases, and then the adsorption capacity of the carbon material with a multilayer structure obtained through simple KOH activation increases to 288.9mg/g.
FIG. 3N was performed on samples of poplar charcoal, delignified poplar charcoal and layered porous biochar from example 2 2 As can be seen from fig. 3, according to International Union of Pure and Applied Chemistry (IUPAC) classification, poplar charcoal and delignified poplar charcoal both show reversible type ii isotherms, indicating typical mesoporous materials. Notably, the delignified poplar charcoal increased adsorption capacity at the initial stage, indicating the presence of micropores. Furthermore, it is evident that the isotherm of the layered porous biochar is a mixture of type I and type IV, with higher absorptivity at lower relative pressures, indicating the creation of abundant micropores. The hysteresis loop between the adsorption and desorption isotherms is more evident, indicating mesoporous development.
FIG. 4 pore size distribution diagrams based on BJH method and DFT method of poplar charcoal, delignified poplar charcoal and layered porous biochar samples in example 2. It is understood from FIG. 4 that delignification and KOH activation improve the mesoporous and microporous volumes of delignified poplar charcoal and layered porous biochar compared to the original poplar charcoal, so that the specific surface area is remarkably increased.
FIG. 5 shows the effect of the layered porous biochar on the adsorption of different initial concentrations of Cr (VI) in example 3, (a) the adsorption amount of the layered porous biochar on the adsorption of different initial concentrations of Cr (VI), and (b) the removal rate of the adsorption of different initial concentrations of Cr (VI) by the layered porous biochar, as shown in FIG. a, the adsorption capacity increased with the increase of the chromium concentration, the adsorption reached equilibrium at about 3 hours when the initial concentration was low, and the adsorption equilibrium time gradually increased when the concentration was higher. As can be seen from FIG. b, when the initial concentration exceeds 60mg/L, the removal rate is lowered because the amount of adsorbent used is small enough to adsorb excessive contaminants. Therefore, in practical use, when treating 1L of wastewater of a relatively high concentration (> 200 mg/L), the amount of the adsorbent to be used is increased to 1g to ensure a relatively high removal effect.
FIG. 6 is an isothermal model fit of the layered porous biochar adsorption Cr (VI) of example 4, and both models were used for fitting and analyzing data (FIG. 6), as can be seen from the figure, the adsorption capacity also increases continuously with increasing temperature, and the Langmuir fitting degree is higher than Freundlich, indicating that the Langmuir model is more suitable for the chromium adsorption process. At 298K, the maximum adsorption of Cr (VI) by ACDW calculated by Langmuir model was 294.86mg/g.
FIG. 7 is a model fit of the kinetics of Cr (VI) adsorption by the layered porous biochar of example 5. As can be seen from FIG. 7, the layered porous biochar has the fastest adsorption rate of Cr within 2 hours and is balanced at about 12 hours. From the fitted data, the pseudo-primary kinetic model is not applicable to the adsorption process, whereas the pseudo-secondary kinetic model is applicable to the adsorption process. The fitting parameters are shown in Table 2, where R is the pseudo-primary dynamics model 2 The value is 0.72, the adsorption capacity is 173.45mg/g, and R of a pseudo-secondary kinetic model 2 The value was 0.96 and the adsorption capacity was 178.92mg/g, which showed that the adsorption process was mainly controlled by chemisorption, as compared to the experimental value 179.9mg/g, which was more consistent with the fitting of the pseudo-secondary kinetic model.
FIG. 8A spectral analysis of the layered porous biochar of example 6 after Cr (VI) adsorption, as can be seen from FIG. 8, the elemental map after the adsorption experiment shows a uniform distribution of C, O, cr elements on the surface of the layered porous biochar (FIGS. 8 a-d). In addition, the EDS spectrum (fig. 8 e) shows that Cr with a mass ratio of 45.14% and an atomic ratio of 17.81% exists in different valence states, and Cr (iii) and Cr (vi) exist, further shows that the layered porous biochar has good adsorption performance, and also shows that some Cr (vi) fixes chromium ions on the surface of the layered porous biochar through reduction reaction with functional groups on the surface of the layered porous biochar.
FIG. 9 is an x-ray photoelectron spectrum after Cr (VI) is adsorbed by the layered porous biochar in example 6, and it is understood from the figure that the characteristic difference of chemical components of the layered porous biochar before and after Cr (VI) is adsorbed is studied by the x-ray photoelectron spectrum, revealing the adsorption mechanism of the layered porous biochar to chromium. The x-ray photoelectron spectra showed that the characteristic spin orbit peaks at 576.38, 580.93 and 586.36eV were Cr (III) and the characteristic spin orbit peaks at 588.86 and 577.79eV were Cr (VI), indicating partial reduction of the original Cr (VI) to lower Cr (III). Furthermore, in c=o (530.84 eV), O-c=o (531.76 eV) and C-O (532.98 eV), the spin-orbit peaks of O1s after Cr adsorption undergo a red shift of binding energy at 529.60, 531.00 and 532.23eV, respectively (fig. 9C-d). This phenomenon may be caused by complex compounds formed by the interaction (e.g., ion exchange) and complexation of lone pair electrons of oxygen-containing groups (i.e., carboxyl and hydroxyl groups) with Cr (VI).
TABLE 1 calculation of sample porosity parameters based on nitrogen adsorption-desorption isotherms
S BET Specific surface area; v (V) tot Total pore volume; v (V) mi Micropore volume; v (V) me Mesopore volume; and D, average pore diameter.
As is clear from Table 1, the poplar charcoal has a compact structure, which results in a small specific surface area, a small total pore volume, and substantially no micropores, and the delignified poplar charcoal formed after delignification has a multi-layer structure, thereby forming more micropores and mesopores, and the micropore volume is increased from 0.008 to 0.036cm 3 g -1 . Resulting in a significant increase in specific surface area without delignification4 times of (2). After activation, more pore structures are added to the original layered structure, and more micropores are generated after activation, so that the diameter of the pores is reduced from 6.36nm to 5.75nm.
TABLE 2 adsorption kinetics of layered porous biochar to adsorb chromium
The fitting parameters of the dynamics are shown in Table 2, where R is the pseudo first order dynamics model 2 The value is 0.72, the adsorption capacity is 173.45mg/g, and R of a pseudo-secondary kinetic model 2 The value was 0.96 and the adsorption capacity was 178.92mg/g, which showed that the adsorption process was mainly controlled by chemisorption, as compared to the experimental value 179.9mg/g, which was more consistent with the fitting of the pseudo-secondary kinetic model.
Claims (4)
1. The application of the layered porous biochar in removing hexavalent chromium in a solution is characterized by comprising the following steps of:
(1) Raw material preparation:
the biomass raw material adopts forestry processing wood chips;
(2) And (3) lignin removal treatment:
removing lignin from the wood chips;
(3) Carbonizing lignin-removed wood chips:
pyrolyzing the delignified wood chips under inert gas to obtain carbonized delignified wood chips;
(4) And (3) activating:
carbonizing lignin-removed wood dust for alkali activation, and then placing the wood dust under inert gas for pyrolysis to obtain layered porous biochar;
the specific process of the delignification treatment in the step (2): with NaOH and Na 2 SO 3 Removing lignin by completely soaking wood chips in the mixed solution, boiling, pouring out waste liquid, boiling and washing with water for multiple times until the washed solution is colorless, and using H 2 O 2 Soaking lignin-removed wood chips in the solution, regulating the pH value of the solution to be alkaline during soaking,finally, cleaning the wood chips with water until the solution is neutral, and drying to obtain delignified wood chips;
in the step (2), 0.1-2 mmol/L NaOH and 0.1-2 mmol/L Na are adopted 2 SO 3 The volume ratio of the two is 0.5: 1-2: 1, a step of;
step (2) adding NaOH and Na 2 SO 3 The reaction is carried out at the temperature of 90-110 ℃, and the waste liquid is poured out after the water bath kettle is boiled for 1-10 hours;
step (2) is performed with 2 to 5 percent of H 2 O 2 Soaking the wood chips subjected to lignin removal for 1-3 hours in the solution, and adding ammonia water to adjust the pH of the solution to 9-11 during soaking; finally, the wood chips are washed by deionized water until the solution is neutral, and the lignin-removed wood chips are obtained by drying.
2. The use according to claim 1, wherein the delignified wood chips in step (3) are subjected to pyrolysis under inert gas, a certain heating rate is maintained, the pyrolysis temperature is 650-750 ℃, and the pyrolysis time is 1-3 hours.
3. The use according to claim 1, wherein step (4) is carried out with KOH; mixing KOH and the prepared carbonized delignified wood chips, grinding uniformly, adding water, stirring for dissolving, and drying;
the pyrolysis temperature in the step (4) is 650-750 ℃ and the pyrolysis time is 1-3 hours;
in the step (4), the mass ratio of KOH/carbonized delignified wood chips=3: 1-5: 1.
4. the use according to claim 1, wherein in step (1) the wood chips are sieved through a 60 mesh sieve, washed with deionized water and ethanol and dried.
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| US4395543A (en) * | 1981-08-12 | 1983-07-26 | Massachusetts Institute Of Technology | Selective solvent extraction of cellulosic material |
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