Felix R. Roman
University of Puerto Rico Mayaguez, Chemistry, Faculty Member
- Education and research training at the University of Puerto Rico at Mayaguezedit
Abstract This work presents the preparation and characterization of a hierarchical porous carbon – Mn+[FAU] or Mn+-CFAU (Mn+ = Ni2+ or Cu2+; FAU = Y zeolite) adsorbent as a potential platform to develop processes for the removal of... more
Abstract This work presents the preparation and characterization of a hierarchical porous carbon – Mn+[FAU] or Mn+-CFAU (Mn+ = Ni2+ or Cu2+; FAU = Y zeolite) adsorbent as a potential platform to develop processes for the removal of contaminants of emerging concern (CECs) from water. The impetus for this contribution is the possibility of combining the hydrophobic nature of activated carbons with the unique adsorbent–adsorbate interactions provided by a transition metal based zeolite. A quasi-ordered (CFAU) composite was hydrothermally synthesized and subsequently decorated with extraframework transition metal centers (Ni2+ or Cu2+). The resulting CFAU variants were fully characterized using XRD, XPS, ICP-MS, TGA, zeta potential and nitrogen adsorption to determine chemical, structural and textural properties. Furthermore, these properties were used to assess the performance of the CFAU variants during salicylic acid (a CEC with high occurrence) equilibrium adsorption tests performed at 25 °C and pH in the 7–8 range. In terms of performance, the salicylic acid equilibrium overall adsorption capacities increased as follows: FAU
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Calcium Alginate/Spent-Coffee-Grounds composite beads (CA-SCGs beads), which were made of two different proportions of alginate and spent-coffee-grounds (3:3 and 3:10), respectively, were used to adsorb Cu2+ in aqueous solution. These... more
Calcium Alginate/Spent-Coffee-Grounds composite beads (CA-SCGs beads), which were made of two different proportions of alginate and spent-coffee-grounds (3:3 and 3:10), respectively, were used to adsorb Cu2+ in aqueous solution. These beads were compared with calcium alginate beads (CA beads) and spent-coffee-grounds (SCGs) in terms of adsorption capacity and rate of adsorption. The experiments were carried out at an initial pH of 4 at 30 °C with initial concentrations of Cu2+ from 10 ppm to 100 ppm. Equilibrium data was fitted with Langmuir, Freundlich and Sips models, and a pseudo-second-order kinetic equation. The Sips model showed the best correlation with the experimental values. CA-SCGs (3:3) beads showed a faster adsorption rate versus the CA beads. Also, CA-SCGs (3:3) beads showed a larger capacity of adsorption according to the Sips model, but not in the Langmuir model. FT-IR spectra and SEM images were taken for characterization. This study has shown that the CA-SCGs (3:3)...
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A. A method was developed for determination of aluminum in biological samples by anion exchange chromatography and neutron activation analysis (NAA). The samples were digested with nitric acid at 65$\sp\circ$C, converting the aluminum to... more
A. A method was developed for determination of aluminum in biological samples by anion exchange chromatography and neutron activation analysis (NAA). The samples were digested with nitric acid at 65$\sp\circ$C, converting the aluminum to Al$\sp{+3}$. The remaining solids were dissolved with dilute tiron solution, and the pH adjusted to six with ammonium hydroxide. The tiron forms a negative complex with aluminum, which is retained on the anion exchange resin. To remove the interfering ions ($\sp{31}$P, $\sp{24}$Na, $\sp{37}$Cl) present in biological material, ammonium citrate was eluted through the resin. The aluminum was stripped from the resin with nitric acid. Fractions eluting from the column were assayed for aluminum content using NAA. The aluminum recoveries were determined to be quantitative by the method of additive spikes. Urine, bone and tissue samples were analyzed for aluminum content. B. Previously reported recoil halogen-for-halogen substitution reactions of diastereom...
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Important for the determination of trace elements, ions, or compounds in urine by chemical neutron activation analysis is the optimization of sample handling, preirradiation chemistry, and radioassay procedures necessary for viable... more
Important for the determination of trace elements, ions, or compounds in urine by chemical neutron activation analysis is the optimization of sample handling, preirradiation chemistry, and radioassay procedures necessary for viable analysis. Each element, because of its natural abundance in the earth's crust and, hence, its potential for reagent and environmental contamination, requires specific procedures for storage, handling, and preirradiation chemistry. Radioassay techniques for radionuclides vary depending on their half-lives and decay characteristics. Described in this paper are optimized procedures for aluminum and selenium. While {sup 28}Al (T{sub 1/2} = 2.24 min) and {sup 77m}Se(T{sub 1/2} = 17.4s) have short half-lives, their gamma-ray spectra are quite different. Aluminum-28 decays by a 1779-keV gamma and {sup 77m}Se by a 162-keV gamma. Unlike selenium, aluminum is a ubiquitous element in the environment requiring special handling to minimize contamination in all pha...
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Pillared clay based composites containing transition metals and a surfactant, namely MAlOr-NaBt (Bt=bentonite; Or=surfactant; M=Ni(2+), Cu(2+)or Co(2+)), were prepared to study selectivity and capacity toward single and multiple-component... more
Pillared clay based composites containing transition metals and a surfactant, namely MAlOr-NaBt (Bt=bentonite; Or=surfactant; M=Ni(2+), Cu(2+)or Co(2+)), were prepared to study selectivity and capacity toward single and multiple-component adsorption of bisphenol A (BPA) and 2,4-diclorophenol (DCP) from water. Tests were also performed to account for the presence of natural organic matter in the form of humic acid (HA). Equilibrium adsorption capacities for single components increased as follows: NaBt<Al-NaBt<AlOr-NaBt<MAlOr-NaBt. The observed equilibrium loadings were ca. 5 and 3mgg(-1) for BPA and DCP, respectively, at neutral pH conditions and ambient temperature, representing an ordered of magnitude increase over the unmodified pillared clay capacities. Inclusion of the transition metal brought an increase of nearly two-fold in adsorption capacity over the materials modified only with surfactant. The MAlOr-NaBt adsorbents displayed remarkable selectivity for BPA. Multi-c...
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Abstract SBA-15 mesoporous silica has been modified in an attempt to develop a platform for adsorbents that can be tailored to target particular contaminants of emerging concern (CECs) present in water sources. Traditionally, mesoporous... more
Abstract SBA-15 mesoporous silica has been modified in an attempt to develop a platform for adsorbents that can be tailored to target particular contaminants of emerging concern (CECs) present in water sources. Traditionally, mesoporous silicas have exhibited less than desired structural stability in the presence of water, but when carefully grafted with amines and transition metal immobilization (Co2+, Ni2+ or Cu2+) the problem can be minimized in a considerable fashion. We have developed a method that combines blockage of surface micropores and transition metal sources containing less hydration levels to avoid depolymerization of the silica wall. This approach enhanced the materials textural properties and, therefore, the adsorption of CECs. At neutral pH and ambient temperature, a better affinity toward acidic and anionic CECs was observed in M-NH2_g_SBA-15 (M = Co2+, Ni2+ or Cu2+) materials whereas a better affinity toward neutral CECs took place in as-prepared SBA-15. The CuNH2_g_SBA-15 variant displayed the best overall adsorption working capacities, probably due to enhanced steric conditions and specific surface interactions. The latter commensurate well with X-ray photoelectron spectroscopy analyses, which showed that copper underwent the most interactions with the surface environment.
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ABSTRACTThe use of nano-sized silver and its alloys represents an interesting alternative to common food preservation methods, which are based on radiation, heat treatment and low temperature storage. These metal nanoparticles, embedded... more
ABSTRACTThe use of nano-sized silver and its alloys represents an interesting alternative to common food preservation methods, which are based on radiation, heat treatment and low temperature storage. These metal nanoparticles, embedded within a polymeric matrix for instance, would extend the shelf life of perishable foods while acting as a bactericidal agent to prevent food-borne illnesses. Common methods used in the synthesis of metal nanoparticles require toxic solvents and reagents that could be harmful to health and the food itself. In addition, several steps are required to obtain aqueous stable, i.e. dispersible, silver nanoparticles. In this work we propose the microwave-assisted aqueous synthesis of silver-based nanoparticles, (Ag Based NP) functionalized by glutathione (GSH) in a single-step using sodium sulfite (Na2SO3), as reducing agent. Ag-Based nanoparticles were synthesized at pH 6 and 1:3:1 (AgNO3/GSH/ Na2SO3) molar ratio. UV-Vis measurement clearly showed the plasm...
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Nanotechnology and its application is one of the rapidly developing sciences. As demand of fresh drinking water is increasing, nanotechnology can contribute noticeable development and improvement to water treatment process. Disinfection... more
Nanotechnology and its application is one of the rapidly developing sciences. As demand of fresh drinking water is increasing, nanotechnology can contribute noticeable development and improvement to water treatment process. Disinfection process is the last and most important step in water and wastewater treatment process. Some nanomaterials can be used as disinfectants due to their antimicrobial properties and reduce the possibility of harmful disinfection by-products (DBPs) formation during traditional disinfection process. A significant number of research efforts is done or going on to understand the mechanisms and enhance the efficiency of nanomaterials as antimicrobial agents, although it will take more time to understand the full potential of nanomaterials in this field. This review paper focuses on inactivation pathways of benign nanomaterials, their possible and probable application and limitations as disinfectants and future opportunities for their application in water cleaning processes.
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This report describes the speciation of arsenic oxyanion mixtures using a liquid chromatography coupled with inductively coupled plasma mass spectrometry (LC-ICPMS) technique. The proposed method allowed a fast, sensitive and... more
This report describes the speciation of arsenic oxyanion mixtures using a liquid chromatography coupled with inductively coupled plasma mass spectrometry (LC-ICPMS) technique. The proposed method allowed a fast, sensitive and environmentally friendly determination of arsenic inorganic species in water. The speciation was carried out during adsorption experiments using dried sludge as an adsorbent. The dried used sludge was generated as discarded material from a water plant after coagulation and sedimentation stages and was selected due to its chemical and mineralogical composition. The sludge composition includes high proportions of silica, aluminium and iron minerals, which are known to be responsible for the adsorption of arsenic species. The As speciation results demonstrated a low limit of detection (LOD) of 5.26 ppb for arsenite and 9.85 ppb for arsenate species. The arsenate species was removed faster compared to the arsenite species when both are present as mixtures. These findings confirm that electrostatic interactions between the sludge components and charged H2AsO4−, arsenate predominant species at pH 6.0, result in a faster equilibrium than H3AsO3 (arsenite, a predominantly neutral species at pH 6.0). The adsorption was fitted by Langmuir and Freundlich models; the second one being the one which better represented the adsorption process. The Freundlich parameter k, the relative uptake capacity of the adsorbent, was 0.221 (mg g−1) (L mg−1)n for arsenite and 0.101 (mg g−1) (L mg−1)n for arsenate. The data from competitive adsorption tests suggested that the removal mechanism for arsenic species is due to the formation of an outer sphere complex via electrostatic or van der Waals attractions. The results show the capability of the dried sludge as a green alternative to remove trace levels of both arsenic oxyanions from contaminated or wastewaters. Also, the developed speciation protocol allowed a better understanding of the adsorption mechanism of arsenic species by Fe-rich sludge.
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ABSTRACT Size-exclusion chromatography (SEC) associated with High Performance Liquid Chromatography (HPLC) is a powerful tool to separate, purify and fractionalize materials based on size. In this paper, we present a SEC method that was... more
ABSTRACT Size-exclusion chromatography (SEC) associated with High Performance Liquid Chromatography (HPLC) is a powerful tool to separate, purify and fractionalize materials based on size. In this paper, we present a SEC method that was developed for the separation of thiol-capped Cd(Se,S) quantum dots (QDs) synthesized in the aqueous phase. A HPLC system with a SEC column and a cascade of three detectors (UV/Vis, FLD and ELSD) was used to analyze the different size fractions of QDs. Nanocrystals–HPLC column interactions were suppressed using thioglycolic acid (TGA) as an ion pair agent. Five fractions, namely F1 to F5, of different sizes and tunable optical properties were isolated from the original QDs sample. The emission peaks for fractions F1 and F2 were red-shifted and the fractions F4 and F5 were blue-shifted compared with the original sample, which suggested the presence of nanocrystals having different sizes. Dynamic Light Scattering (DLS) confirmed that collected fractions exhibited different hydrodynamic diameters ranging from 98.2 nm (fraction F1) to 24.9 nm (fraction F5). Also, fractions F2 and F4 were functionalized with glutathione and analyzed by HPLC-SEC. Glutathione-capped Cd(Se,S) QDs showed an increase in their molecular weight, when compared to bare TGA-capped Cd(Se,S) QDs, without a remarkable change of their crystal size and optical properties. The developed SEC technique allows a fast and reproducible separation of water-stable Cd(Se,S) QDs. Collected fractions with tunable optical properties could have potential applications in the nanotechnology area such as bio-imaging and diagnostics, e.g. cell sorting.
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Quantum dots of Cd(Se,S) and fluorescent magnetic nanocomposites (Cd(Se,S)–magnetite) were used as photocatalytic agents in the photodegradation of methylene blue (MB) under UV irradiation at pH 6.5. Quantum dots and magnetic... more
Quantum dots of Cd(Se,S) and fluorescent magnetic nanocomposites (Cd(Se,S)–magnetite) were used as photocatalytic agents in the photodegradation of methylene blue (MB) under UV irradiation at pH 6.5. Quantum dots and magnetic nanocomposites were characterized by X-ray diffraction (XRD), UV-Vis, photoluminescence and Fourier Transform Infrared (FT-IR) spectroscopy. The photo-induced degradation of MB was monitored using High Performance Liquid Chromatography (HPLC) at 660 nm and titanium dioxide (anatase and aeroxide P25 forms) was used as the photocatalyst standard. A degradation of 99.1% and 90.0% of MB was achieved in the presence of 160 mg L−1-quantum dots and the magnetic nanocomposite, respectively, after 4.5 hours of UV-irradiation. Instead, 45.9% and 100% of MB degradation was achieved using 160 mg L−1 of TiO2 anatase and aeroxide P25, respectively. The degradation products were studied by mass spectrometry (MS) and the results evidenced the formation of azure B, A, C and phe...
Copper-doped quantum dots of ZnSe(S) synthesized via microwave-heating conditions were used as photocatalyst in the photo-degradation of methylene blue (MB), methyl violet (MV) and victoria blue (VB) under UV irradiation (302 nm) in... more
Copper-doped quantum dots of ZnSe(S) synthesized via microwave-heating conditions were used as photocatalyst in the photo-degradation of methylene blue (MB), methyl violet (MV) and victoria blue (VB) under UV irradiation (302 nm) in aqueous phase and at pH 6.5. Quantum dots were characterized by High Resolution Transmission Electron Microscopy (HR-TEM), X-ray diffraction (XRD), UV-Vis, photoluminescence and Fourier transform infrared (FT-IR) spectroscopy. The degradation of MB, MV and VB were monitored using High Performance Liquid Chromatography (HPLC) at 660 nm, 590 nm and 610 nm, respectively. Degradations percentages of 46%, 88% and 90% of MB, MV and VB, respectively, were achieved in presence of 1000 mg/L of quantum dots and 6 hours of UV-irradiation. Cu-doped ZnSe(S) QDs evidenced a remarkable capability to degrade cationic organic dyes as single components and in mixtures.
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Fixed-beds of transition metal (Co(2+), Ni(2+) or Cu(2+)) inorganic-organic pillared clays (IOCs) were prepared to study single- and multi-component non-equilibrium adsorption of a set of pharmaceutical and personal care products (PPCPs:... more
Fixed-beds of transition metal (Co(2+), Ni(2+) or Cu(2+)) inorganic-organic pillared clays (IOCs) were prepared to study single- and multi-component non-equilibrium adsorption of a set of pharmaceutical and personal care products (PPCPs: salicylic acid, clofibric acid, carbamazepine and caffeine) from water. Adsorption capacities for single components revealed that the copper(II) IOCs have better affinity toward salicylic and clofibric acid. However, multi-component adsorption tests showed a considerable decrease in adsorption capacity for the acids and an unusual selectivity toward carbamazepine depending on the transition metal. This was attributed to a combination of competition between PPCPs for adsorption sites, adsorbate-adsorbate interactions, and plausible pore blocking caused by carbamazepine. The cobalt(II) IOC bed that was partially calcined to fractionate the surfactant moiety showcased the best selectivity toward caffeine, even during multi-component adsorption. This was due to a combination of a mildly hydrophobic surface and interaction between the PPCP and cobalt(II). In general, the tests suggest that these IOCs may be a potential solution for the removal of PPCPs if employed in a layered-bed configuration, to take care of families of adsorbates in a sequence that would produce sharpened concentration wavefronts.
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The Energy Citations Database (ECD) provides access to historical and current research (1948 to the present) from the Department of Energy (DOE) and predecessor agencies.
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Research Interests: Organic Chemistry, Electrochemistry, Mass Spectrometry, NMR Spectroscopy, Cyclic Voltammetry, and 10 moreMagnetic Resonance Spectroscopy, DNA, Potentiometry, Hydrogen Bonding, Bioorganic and medicinal Chemistry, Organometallic Compounds, Hydrogen-Ion Concentration, Protons, Oligonucleotides, and Molecular Structure
Characterization and differentiation of high energy cyclic organic peroxides by GC/FT-IR, GC-MS, FT-IR, and Raman microscopy. [Proceedings of SPIE 5778, 347 (2005)]. Alvaro J. Pena, Leonardo Pacheco-Londono, Javier Figueroa ...
Research Interests: Thermodynamics, Microscopy, Kinetics, Raman Spectroscopy, Vibration, and 14 moreTime-of-flight mass spectrometry, Proceedings, Household Production, Differentiation, Real Time, Raman microscopy, Development Methodology, Retention Time, Infrared Spectrometry, Mixture, Chemical Synthesis, Fourier Transformation, High energy, and Secondary production
As part of our research efforts in the area of titanium-based antitumor agents, we have investigated the cytotoxic activity of [Ti(4)(maltolato)(8)(mu-O)(4)], (Cp-R)(2)TiCl(2) and (Cp-R)CpTiCl(2) (R = CO(2)CH(3) and CO(2)CH(2)CH(3)), and... more
As part of our research efforts in the area of titanium-based antitumor agents, we have investigated the cytotoxic activity of [Ti(4)(maltolato)(8)(mu-O)(4)], (Cp-R)(2)TiCl(2) and (Cp-R)CpTiCl(2) (R = CO(2)CH(3) and CO(2)CH(2)CH(3)), and three water-soluble titanocene-amino acid complexes-[Cp(2)Ti(aa)(2)]Cl(2) (aa = L: -cysteine, L: -methionine, and D: -penicillamine)-on the human colon adenocarcinoma cell line, HT-29. The capacity of [Ti(4)(maltolato)(8)(mu-O)(4)] to donate Ti(IV) to human apo-transferrin and its hydrolytic stability have been investigated and compared to the previously reported data on modified titanocenes with either hydrophilic ancillary ligands or the functionalized cyclopentadienyl ligands. Notably, the titanium-maltolato complex does not transfer Ti(VI) to human apo-transferrin at any time within the first seven days of its interaction, demonstrating the inert character of this species. Stability studies on these complexes have shown that titanocene complexes decompose at physiological pH while the [Ti(4)(maltolato)(8)(mu-O)(4)] complex is stable at this pH without any notable decomposition for a period of ten days. The antitumor activity of these complexes against colon cancer HT-29 cells was determined using an MTT cell viability assay at 72 and 96 h. The titanocene-amino acid and the (Cp-R)(2)TiCl(2)/(Cp-R)CpTiCl(2) (R = CO(2)CH(3)) complexes were not biologically active when human transferrin was absent; they also were inactive when human transferrin was present at dose-equivalent concentrations. (Cp-R)(2)TiCl(2) and (Cp-R)CpTiCl(2) (R = CO(2)CH(2)CH(3)) showed cytotoxic activity in HT-29 cells comparable to that which is displayed by titanocene dichloride. The titanium-maltolato complex had higher levels of cytotoxic activity than any other titanocene complex investigated. Transferrin may be important in protecting the titanium center from hydrolysis, but this may be achieved by selecting ligands that could result in hydrolytically stable, yet active, complexes.
Research Interests: Inorganic Chemistry, Titanium, Magnetic Resonance Spectroscopy, Cell line, Humans, and 19 moreBiological, Transferrin, Cell Viability, Cytotoxic Activity, Solutions, Colon cancer, Amino Acid Profile, Water soluble polymers, Molecular Conformation, Biological activity, Thiazoles, Antitumor Activity, Structure activity Relationship, Organometallic Compounds, Drug Stability, Antineoplastic Agents, Ligands, Biochemistry and cell biology, and Apoproteins
Since aluminum is an extremely difficult element to determine reliably in biological samples, no National Institute of Standards and Technology (NIST) biological standard reference material for tissue has yet been certified for aluminum.... more
Since aluminum is an extremely difficult element to determine reliably in biological samples, no National Institute of Standards and Technology (NIST) biological standard reference material for tissue has yet been certified for aluminum. A chemical neutron activation analysis procedure employing anion-exchange chromatography was developed. The procedure proved successful in decontaminating radioactivatable sodium and chlorine and phosphorus which can produce aluminum via a fast neutron bombardment. For bovine liver (NIST SRM 1577 a) a value of 2.1 +/- 0.2 micrograms of aluminum/g of sample was determined, comparing favorably to the uncertified value 2 micrograms/g sample. For freeze-dried urine (NIST SRM 2670) a value of 0.18 +/- 0.01 micrograms of aluminum/mL of urine was observed. Its uncertified value is 0.18 micrograms of aluminum/mL of sample. Twenty three individual samples in three different human brains were analyzed for their aluminum content.