Md. Selim Arif Sher Shah

Green Synthesis of Biphasic TiO2–Reduced Graphene Oxide Nanocomposites with Highly Enhanced Photocatalytic Activity

A series of TiO(2)-reduced graphene oxide (RGO) nanocomposites were prepared by simple one-step hydrothermal reactions using the titania precursor, TiCl(4) and graphene oxide (GO) without reducing agents. Hydrolysis of TiCl(4) and mild reduction of GO were simultaneously carried out under hydrothermal conditions. While conventional approaches mostly utilize multistep chemical methods wherein strong reducing agents, such as hydrazine, hydroquinone, and sodium borohydride are employed, our method provides the notable advantages of a single step reaction without employing toxic solvents or reducing agents, thereby providing a novel green synthetic route to produce the nanocomposites of RGO and TiO(2). The as-synthesized nanocomposites were characterized by several crystallographic, microscopic, and spectroscopic characterization methods, which enabled confrimation of the robustness of the suggested reaction scheme. Notably, X-ray diffraction and transmission electron micrograph proved that TiO(2) contained both anatase and rutile phases. In addition, the photocatalytic activities of the synthesized composites were measured for the degradation of rhodamine B dye. The catalyst also can degrade a colorless dye such as benzoic acid under visible light. The synthesized nanocomposites of biphasic TiO(2) with RGO showed enhanced catalytic activity compared to conventional TiO(2) photocatalyst, P25. The photocatalytic activity is strongly affected by the concentration of RGO in the nanocomposites, with the best photocatalytic activity observed for the composite of 2.0 wt % RGO. Since the synthesized biphasic TiO(2)-RGO nanocomposites have been shown to effectively reduce the electron-hole recombination rate, it is anticipated that they will be utilized as anode materials in lithium ion batteries.

Single-step solvothermal synthesis of mesoporous Ag–TiO2–reduced graphene oxide ternary composites with enhanced photocatalytic activity

With growing interest in the photocatalytic performance of TiO2-graphene composite systems, the ternary phase of TiO2, graphene, and Ag is expected to exhibit improved photocatalytic characteristics because of the improved recombination rate of photogenerated charge carriers and potential contribution of the generation of localized surface plasmon resonance at Ag sites on a surface of the TiO2-graphene binary matrix. In this work, Ag-TiO2-reduced graphene oxide ternary nanocomposites were successfully synthesized by a simple solvothermal process. In a single-step synthetic procedure, the reduction of AgNO3 and graphene oxide and the hydrolysis of titanium tetraisopropoxide were spontaneously performed in a mixed solvent system of ethylene glycol, N,N-dimethylformamide and a stoichiometric amount of water without resorting to the use of typical reducing agents. The nanocomposites were characterized by X-ray diffraction, X-ray photoelectron spectroscopy, along with different microscopic and spectroscopic techniques, enabling us to confirm the successful reduction of AgNO3 and graphite oxide to metallic Ag and reduced graphene oxide, respectively. Due to the highly facilitated electron transport of well distributed Ag nanoparticles, the synthesized ternary nanocomposite showed enhanced photocatalytic activity for degradation of rhodamine B dye under visible light irradiation.

Highly efficient and recyclable nanocomplexed photocatalysts of AgBr/N-doped and amine-functionalized reduced graphene oxide.

Although silver bromide has recently drawn considerable attention because of its high photocatalytic activity, it tends to form agglomerated metallic silver under the irradiation of visible light. Therefore, photocatalytic activity decreases with time and cannot be applied for repeated uses. To overcome this limitation, in the present work, we complexed AgBr with nitrogen doped (N-doped) and amine functionalized reduced graphene oxide (GN). N-doped and/or amine functionalized graphene shows intrinsically good catalytic activity. Besides, amine groups can undergo complexation with silver ions to suppress its reduction to metallic Ag. As a result, these complexed catalysts show excellent photocatalytic activity for the degradation of methylene blue (MB) dye under the irradiation of visible light. Photocatalytic degradation of MB shows that the catalytic activity is optimized at a condition of 0.5 wt % GN, under which ∼99% of MB was degraded only after 50 min of visible light irradiation. Notably, the complexed catalyst is quite stable and retained almost all of its catalytic activity even after greater than 10 repeated cycles. Moreover, the catalyst can also efficiently decompose 2-chlorophenol, a colorless organic contaminant, under visible light exposure. Detailed experimental investigation reveals that hydroxyl (·OH) radicals play an important role for dye degradation reactions. A relevant mechanism for dye degradation has also been proposed.

Incorporation of PEDOT:PSS into SnO2/reduced graphene oxide nanocomposite anodes for lithium-ion batteries to achieve ultra-high capacity and cyclic stability

SnO2, a candidate material for anodes in Li-ion batteries (LIBs), usually suffers from severe volume change (>300%) during charge–discharge cycles. This problem leads to undesirable continuous capacity fading, hindering its practical utilization. To address this issue, nanostructured SnO2 and its composites with carbon nanomaterials, especially graphene, have extensively been studied. Although the stability issue has improved substantially, these materials still suffer from low capacity characteristics, which are far from the theoretical capacity of SnO2. Motivated by this background, in this work, we synthesized a novel ternary nanocomposite of SnO2, reduced graphene oxide (rGO), and a conducting polymer, poly(3,4-ethylenedioxythiophene)-poly(styrenesulfonate) (PEDOT:PSS), as a high performance anode material in LIBs. PEDOT:PSS together with rGO is expected to efficiently accommodate the volume change in SnO2 during cycling. Transmission electron microscopic observation reveals 2–3 nm-sized SnO2 nanoparticles are uniformly dispersed over rGO nanosheets while having a PEDOT:PSS coating. The capacities of the synthesized composites were dependent on the PEDOT:PSS concentration. The reversible capacity of the composite with 5 wt% PEDOT:PSS was maintained at 980 mA h g−1 with a coulombic efficiency over 99% even after 160 cycles. This capacity value is equivalent to 1185 mA h g−1 on the basis of only SnO2 in the composite. The high capacity of the ternary nanocomposites is attributed to the ultra-small size of SnO2 nanoparticles, enhanced electronic and ionic mobility, and facilitated volumetric relaxation synergistically offered by rGO nanosheets and the PEDOT:PSS coating.

Non-stoichiometric SnS microspheres with highly enhanced photoreduction efficiency for Cr(VI) ions

Self-doped semiconductors have recently attracted extensive interest as highly efficient photocatalytic materials because the electronic properties can be modulated without sacrificing the chemical stability of the parent material. In this report, we report the facile synthesis of Sn2+ self-doped SnS microparticles via a simple template-free hydrothermal route. Because of the ability to successfully tune the band structure while minimizing defect generation, self-doped SnS could potentially serve as an efficient photocatalyst of wastewater. Here, Sn2+ self-doping results in insertion of an energy level slightly below the conduction band of SnS, thereby decreasing the photoexcitation energy. Furthermore, dopant sites can act as charge trapping sites, which can consequently minimize problematic charge recombination. Synthesized materials were characterized by various spectroscopic, microscopic, and surface characterization techniques, all of which confirmed the formation of self-doped SnS. The Sn2+ self-doped SnS photocatalyst successfully reduced carcinogenic Cr(VI) to the water-insoluble Cr(III) form under visible light illumination. The best photocatalytic efficiency was obtained from an optimal balance between increased numbers of trapping sites leading to longer charge carrier lifetime, and decreased distance between trapping sites, favoring charge recombination. We anticipate that similar methodologies can be applied to other non-stoichiometric semiconducting photocatalysts with tunable electronic properties and enhanced photocatalytic efficiency.