Karim Khan

The technological evolution has been progressing for centuries and will possibly increase at a higher rate in the 21st century. Currently, in this age of nanotechnology, the discovery of more economical and sustainable novel materials has considerably increased. The abundance of two-dimensional (2D) materials has endowed them with a broad material platform in technical studies and in the expansion of nano-and atomic-level applications. The innovation of graphene has motivated considerable attention to the study of other novel 2D materials, known as modern day ''alchemy'', by which scientists are trying to convert most possible periodic table elements into 2D material structures and forms. 2D material devices with high quality and good optical encoder performance have a multitude of industrial applications. However, their stability and large size restrict their applications, but these problems can be overcome by functionalization and substrate-based formation of 2D materials. Therefore, via this review, first, basic attributes of 2D materials are described, and the mechanisms to further enhance their properties are also summarized. Second, the applications of 2D materials are discussed, along with their advantages and disadvantages. Finally, some effective device-fabrication approaches, such as heterostructure approaches, are applied to further enhance the properties of 2D materials; their novel device applications and opportunities are also presented. This updated review may provide new avenues for 2D material synthesis and development of more efficient devices compared to conventional devices in different fields.

An overview of the general importance of 2D monoelemental materials (Xenes) is provided. A summary of the latest development in the group IV Xenes, ranging from synthesis, structures, and properties suitable for sensing applications is also given. A discussion of the applications, challenges, and future directions of the group IV Xenes especially sensing nature of 2D Xenes is presented.

The innovation of the graphene (G) marks key revolutionary events in the science and technology. The normal materials conversion to the two dimensional materials (2DMs), is known as modern day "alchemy" was extended to the most of groups in periodic table. The monoelemental, atomically thin 2DMs, called "Xenes" ("ene" Latin word, means nanosheets (NSs), here, X = different possible group elements (group-IIIA-IVA)) are newly invented edge of the materials family in which one of the most active area is 2DMs investigation. The 2D-Xenes material offers novel properties for the modern nanodevices applications. Any new form of the 2DMs entry into mainstream Xenes would likely compete with today's electronic technology. The metallic 2D-borophene is experimentally formed; subsequent by the theoretical calculations has high in-plane anisotropy together with numerous enviable features like, the 2D-G and phosphorene (2D-BP). As a synthetic 2DMs, the structural properties of 2D-borophene cannot be deduced from bulk boron (B), means that the fundamental defects of the 2D-borophene persisted unknown. The modern highly sensitive potential synthesis and characterization techniques offer an opportunity for investigating the theoretically predicted 2D-Xenes, with atomic precision under idealized conditions. Experimental based theoretically predicted, synthetic 2D-Xenes of the group-IIIA (Borophene (2D-B)) material has been investigated, just like a metallic material. Thus, it is potentially rendering them as potential candidates for the future electrocatalytic based nanodevices, especially potential applications as a catalyst, electrode material, energy storage materials in batteries/superconductors, and so on. In this topical review, we will briefly present various aspects of the 2D-borophene, group-IIIA 2D-Xenes. Thereafter, we will explain different potential methods to synthesize 2D-borophene Xenes, provide a concise summary of the main achievements about their properties, that have been obtained by theoretical simulations as well as by experimental investigations and finally we will discuss the potential applications of the 2D-borophene Xenes, for fundamentally oriented studies. Although, this material investigations and devices applications are still at an early stage, but theoretical calculations and some experimental measurements, provided that, it is complementary to normally used electrocatalytic nanomaterials as well as 2DMs (i.e., layered bulk-derived), with their novel properties and predicted applications.

The successful photo‑catalyst library gives signifcant infor‑
mation on feature that afects photo‑catalytic performance and proposes new
materials. Competency is considerably signifcant to form multi‑functional
photo‑catalysts with fexible characteristics. Since recently, two‑dimensional
materials (2DMs) gained much attention from researchers, due to their unique
thickness‑dependent uses, mainly for photo‑catalytic, outstanding chemical and
physical properties. Photo‑catalytic water splitting and hydrogen  (H2) evolu‑
tion by plentiful compounds as electron  (e−) donors is estimated to participate
in constructing clean method for solar  H2‑formation. Heterogeneous photo‑
catalysis received much research attention caused by their applications to tackle
numerous energy and environmental issues. This broad review explains pro‑
gress regarding 2DMs, signifcance in structure, and catalytic results. We will
discuss in detail current progresses of approaches for adjusting 2DMs‑based
photo‑catalysts to assess their photo‑activity including doping, hetero‑structure
scheme, and functional formation assembly. Suggested plans, e.g., doping and sensitization of semiconducting 2DMs, increasing electrical
conductance, improving catalytic active sites, strengthening interface coupling in semiconductors (SCs) 2DMs, forming nano‑structures,
building multi‑junction nano‑composites, increasing photo‑stability of SCs, and using combined results of adapted approaches, are summed
up. Hence, to further improve 2DMs photo‑catalyst properties, hetero‑structure design‑based 2DMs’ photo‑catalyst basic mechanism is
also reviewed.

In this study, we synthesized nanosized Sn-doped C12A7:e− (C12Al7−xSnx:e−, where x = 0.20 to 1) compo-
site with high surface area of 244 m2
g−1
. An increasing trend in conductivity of Sn-doped C12A7:e− com-
posites was observed at 300 K: 24 S cm−1
,68Scm−1
, 190 S cm−1
and 290 S cm−1
, at doping levels of
x = 0.20, 0.40, 0.80, and 1, respectively. Sn-doped C12A7:e−, with and without reduced graphene oxide
(rGO), acts as a less expensive and highly active and durable electrocatalyst in the oxygen reduction reac-
tion (ORR) for fuel cells. In the case of C12A7−xSnx:e− (where x = 1), calculated onset potential and current
density were comparable to the commercially available 20% Pt/C electrode. Moreover, significant
improvement was observed for Sn-doped C12A7:e− (doping level x = 1) with rGO composite. The ORR
current density was about 5.9 mA cm−2
, which was higher than that of Pt/C (5.2 mA cm−2
). Our investi-
gation of the effect of cation doping on structural and electrical properties of Sn-doped C12A7:e− com-
posites shows that these results manifested the feasibility of this sol–gel method for different element
doping. Furthermore, the as-prepared promising non-noble metal catalysts (NNMCs), viz., Sn-doped
C12A7:e− composite materials, possess intrinsic long-time stability and excellent methanol resistance
toward ORR in alkaline media and may serve as a promising alternative to Pt/C materials for ORR in its
widespread implementation in fuel cells.

The technological evolution has been progressing for centuries and will possibly increase at a higher rate in the 21st century. Currently, in this age of nanotechnology, the discovery of more economical and sustainable novel materials has considerably increased. The abundance of two-dimensional (2D) materials has endowed them with a broad material platform in technical studies and in the expansion of nano-and atomic-level applications. The innovation of graphene has motivated considerable attention to the study of other novel 2D materials, known as modern day ''alchemy'', by which scientists are trying to convert most possible periodic table elements into 2D material structures and forms. 2D material devices with high quality and good optical encoder performance have a multitude of industrial applications. However, their stability and large size restrict their applications, but these problems can be overcome by functionalization and substrate-based formation of 2D materials. Therefore, via this review, first, basic attributes of 2D materials are described, and the mechanisms to further enhance their properties are also summarized. Second, the applications of 2D materials are discussed, along with their advantages and disadvantages. Finally, some effective device-fabrication approaches, such as heterostructure approaches, are applied to further enhance the properties of 2D materials; their novel device applications and opportunities are also presented. This updated review may provide new avenues for 2D material synthesis and development of more efficient devices compared to conventional devices in different fields.

In the present study we synthesized conductive nanoscale [Ca 24 Al 28 O 64 ] 4+ (4e À) (hereafter denoted as C 12 A 7 :e À) material, and reduced graphene oxide (rGO) was produced, which was unexpected; graphene oxide was removed after melting the sample. The conductivity of C 12 A 7 :e À composites synthesized at 1550 C was 1.25 S cm À1 , and the electron concentration was 5.5 Â 10 19 cm À3. The estimated BET specific surface area of the highly conductive sample was 20 m 2 g À1. Pristine C 12 A 7 :e À electride was obtained by melting the composite powder, but the nano size of C 12 A 7 :e À particles could not be preserved; the value of conductivity was $28 S cm À1 , electron concentration was $1.9 Â 10 21 cm À3 , and mass density was 93%. For C 12 A 7Àx V x :e À , where x ¼ 0.25 to 1, the conductivity improved to a maximum value of 40 S cm À1 , and the electron density improved to $2.2 Â 10 21 cm À3 ; this enhancement in conductivity was also proposed by a theoretical study but lacked any associated experimental support.

The 2D graphene (G) nanosheets (NSs) discovery is amound the foremost revolu-
tionary incidents in materials science history. This discovery has stimulated huge
attention in the study of other novel 2D materials (2DMs). This trend might be
called modern day “alchemy,” where the basic aim is to convert most of periodic
table elements into G like 2D structures. Monoelemental, atomically thin 2DMs,
called “Xenes” (“X” = group (III–VI)A elements, “ene”  suffix that indicates one
atom thick 2D layer of atoms) which are a newly invented family among nano-
materials. The number of predicted and experimentally synthesized 2D Xene
materials of group IVA, i.e., G’s siblings, has gained attention in nanosize devices.
Such materials involve buckle structures that have recently been experimentally
fabricated. The 2D Xene materials analog to G offer exciting potential for novel
sensing applications. The group IVA Xenes, in cooperation with their ligand-
functionalized derivatives, arrange in a honeycomb lattice analogous to G but
through a changeable degree of buckling. Their electronic structure ranges from
trivial insulators passing via semiconductors with tunable gaps, to semimetallic,
depending on substrate, chemical functionalization, and strain. In this review, dif-
ferent potential synthesis methods for group IVA 2D Xenes are briefly presented.
A brief overview of their properties obtained theoretically and experimentally is
presented, and finally their potential sensing applications are discussed.