Minuscule weight percent of graphene oxide and reduced graphene oxide modified Ag3PO4: new insight into improved photocatalytic activity

Designing and fabricating hybrid systems with a visible light active semiconductor as one of its components is an important research area for the development of highly efficient photocatalysts. Herein, we report visible-light driven photocatalytic activity of graphene oxide (GO) and controllably reduced GO (rGO) modified Ag3PO4 composites fabricated by an in situ method. Concentration of graphene derivatives in GO/rGO-Ag3PO4 composites was in the range of 0.13-0.52 wt% which is very minute compared to those reported previously. The optimal concentration of GO in Ag3PO4 with a kinetics (k = 1.23 +/- 0.04 min(-1)) for the degradation of rhodamine B is 0.26 wt%. GO-Ag3PO4 photocatalysts display an improved catalytic activity compared with pristine and rGOs modified Ag3PO4. In line with this, GO/rGO-Ag3PO4 composites show improved photocatalytic activity for the degradation of 2-chlorophenol compared with Degussa P-25. Our experiments with GO reduced to different extents show that, rGO with more polar functional groups exhibits a higher photocatalytic efficiency. The photocatalytic activity in the presence of different scavengers reveals that holes and O-2(-center dot) reactive species play major roles in the degradation phenomenon. In view of our experimental results and reported theoretical studies, a change in conduction band energy level and variation in the contribution of different charge orbitals (C 2p and O 2p) to the conduction band in the composite favours electron flow from graphene derivatives to the semiconductor, enhancing its photocatalytic response

Facile synthesis of reduced graphene oxide/Pt-Ni nanocatalysts: their magnetic and catalytic properties

The catalytic performance of metals can be enhanced by intimately alloying different metals with Reduced Graphene Oxide (RGO). In this work, we have demonstrated a simplistic in situ one-step reduction approach for the synthesis of RGO/Pt-Ni nanocatalysts with different atomic ratios of Pt and Ni, without using any capping agent. The physical properties of the as-synthesized nanocatalysts have been systematically investigated by XRD, FTIR, Raman spectroscopy, XPS, EDX, ICP-AES, and TEM. The composition dependent magnetic properties of the RGO/Pt-Ni nanocatalysts were investigated at 5 and 300 K, respectively. The results confirm that the RGO/Pt-Ni nanocatalysts show a super-paramagnetic nature at room temperature in all compositions. Furthermore, the catalytic activities of the RGO/Pt-Ni nanocatalysts were investigated by analyzing the reduction of p-nitrophenol, and the reduction rate was found to be susceptible to the composition of Pt and Ni. Moreover, it has been found that RGO/Pt-Ni nanocatalysts show superior catalytic activity compared with the bare Pt-Ni of the same composition. Interestingly, the nanocatalysts can be readily recycled by a strong magnet and reused for the next reactions

Highly efficient and simultaneous catalytic reduction of multiple dyes using recyclable RGO/Co dendritic nanocomposites as catalyst for wastewater treatment

Development of a low cost, highly efficient and easily retrievable catalyst with improved reusability is a major challenge in the area of advanced catalysts. In this study, we report a simple one-step approach for the fabrication of a reduced graphene oxide (RGO)/Co dendritic nanocomposite. The structure and morphology of the as synthesized material are thoroughly examined by XRD, Raman, FTIR, TEM, and SEM. The magnetic properties of the RGO/Co dendritic nanocomposite reveal that it exhibits ferromagnetic behavior at room temperature with high saturation magnetization. The catalytic activity of the RGO/Co dendritic nanocomposite was investigated for the reduction of different dyes namely, 4-nitrophenol, methylene blue, methyl orange and rhodamine B individually, and their mixture in the presence of a sufficient amount of NaBH4. RGO/Co dendritic nanocomposite exhibits excellent catalytic activity as compared to the bare Co dendritic structure. The catalyst could be easily separated by an external magnet and recycled magnetically with no major loss of catalytic activity upto five cycles. The high catalytic efficiency, low cost and easy recycle technique make RGO/Co dendritic nanocomposite a proficient catalyst for degradation of organic dyes

Ice-templating synthesis of macroporous noble metal/3D-graphene nanocomposites: their fluorescence lifetimes and catalytic study

Porous architectures of 3D-graphene assembled with noble metal (Au, Pd and Pt) nanoparticles were successfully fabricated through a one-step green route using a low-cost freeze-casting method. The as-synthesized noble metal/3D-graphene nanocomposites exhibit ultralow density and interconnected 3-D porous networks with a uniform distribution of noble metal nanoparticles. Time-correlated single photon counting (TCSPC) measurements reveal the energy and electron transfer at the interface of the graphene sheets and noble metals, which is maximum in the case of Pt/3D-graphene due to the small size of the Pt nanoparticles. The as-obtained noble metal/3D-graphene nanocomposites were applied to the reduction of 4-nitrophenol and methylene blue by NaBH4. The rates of reduction are in the order Pt/3D-graphene > Pd/3D-graphene > Au/3D-graphene for both the reduction reactions, signifying that the smallest noble metal nanoparticles possess the highest catalytic activity. The Pt/3D-graphene nanocomposite also exhibits excellent catalytic activity in comparison to the RGO/Pt nanocomposite, which is due to its unique 3D-porous structure. Moreover, the Pt/3D-graphene nanocomposite could be easily separated from the reaction solution by simple filtration and recycled for five cycles without the loss of its catalytic activity. Noble metal/3D-graphene nanocomposites can be utilized as attractive, low-cost, efficient fixed bed reactors and as easily separable catalysts in industrial applications for the reduction of 4-nitrophenol and methylene blue with high catalytic activity and exceptional absorption capability

Controlling Light Absorption in Charge-Separating Core/Shell Semiconductor Nanocrystals

Semiconductor nanocrystals of different formulations have been extensively studied for use in thin-film photovoltaics. Materials used in such devices need to satisfy the stringent requirement of having large absorption cross sections. Hence, type-II semiconductor nanocrystals that are generally considered to be poor light absorbers have largely been ignored. In this article, we show that type-II semiconductor nanocrystals can be tailored to match the light-absorption abilities of other types of nanostructures as well as bulk semiconductors. We synthesize type-II ZnTe/CdS core/shell nanocrystals. This material is found to exhibit a tunable band gap as well as absorption cross sections that are comparable to (die. This result has significant implications for thin-film photovoltaics, where the use of type-II nanocrystals instead of pure semiconductors can improve charge separation while also providing a much needed handle to regulate device composition

Competing Roles of Substrate Composition, Microstructure, and Sustained Strontium Release in Directing Osteogenic Differentiation of hMSCs

Strontium releasing bioactive ceramics constitute an important class of biomaterials for osteoporosis treatment. In the present study, we evaluated the synthesis, phase assemblage, and magnetic properties of strontium hexaferrite, SrFe₁₂O₁₉, (SrFe) nanoparticles. On the biocompatibility front, the size- and dose-dependent cytotoxicity of SrFe against human mesenchymal stem cells (hMSCs) were investigated. After establishing their non-toxic nature, we used the strontium hexaferrite nanoparticles (SrFeNPs) in varying amount (<i>x</i> = 0, 10, and 20 wt %) to consolidate bioactive composites with hydroxyapatite (HA) by multi-stage spark plasma sintering (SPS). Rietveld refinement of these spark plasma sintered composites revealed a near complete decomposition of SrFe₁₂O₁₉ to magnetite (Fe₃O₄) along with a marked increase in the unit cell volume of HA, commensurate with strontium-doped HA. The cytocompatibility of SrHA-Fe composites with hMSCs was assessed using qualitative and quantitative morphological analysis along with phenotypic and genotypic expression for stem cell differentiation. A marked decrease in the stemness of hMSCs, indicated by reduced vimentin expression and acquisition of osteogenic phenotype, evinced by alkaline phosphatase (ALP) and collagen deposition was recorded on SrHA-Fe composites in osteoinductive culture. A significant upregulation of osteogenic marker genes (Runx2, ALP and OPN) was detected in case of the SrHA-Fe composites, whereas OCN and Col IA expression were similarly high for baseline HA. However, matrix mineralization was elevated on SrHA-Fe composites in commensurate with the release of Sr²⁺ and Fe²⁺. Summarizing, the current work is the first report of strontium hexaferrite as a non-toxic nanobiomaterial. Also, SrHA-based iron oxide composites can potentially better facilitate bone formation, when compared to pristine HA