Layered Molybdenum (Meta)phosphate for Photoreduction of Hexavalent Chromium and Degradation of Methylene Blue under Sunlight Radiance.

Noble metal, semiconductor, or metal-free nanomaterials have shown promising applicability as potential photocatalyst materials. A one-step process has been established for the synthesis of layered molybdenum (meta)phosphate [MoO2(PO3)2] using a solvothermal method. The nanopowders were characterized by X-ray diffraction (XRD), UV-visible spectroscopy (UV-vis), scanning electron microscopy (SEM), infrared spectroscopy (IR), X-ray photoelectron spectroscopy (XPS), photoluminescence spectroscopy (PL), surface area analysis (Brunauer-Emmett-Teller (BET)), electron spin resonance (ESR), and high-resolution transmission electron microscopy (HRTEM). Through this study, we demonstrate the use of MoO2(PO3)2 as a photocatalyst for wastewater treatment. The photoreduction of toxic Cr6+ to Cr3+ by layered molybdenum (meta)phosphate is investigated using formic acid as a scavenger. This catalyst has also been used for photodegrading organic dyes like methylene blue. MoO2(PO3)2 has been shown to complete photoreduction of toxic Cr6+ to Cr3+ in 6 min and achieved 78% degradation efficiency for methylene blue in 36 min. The reactive species trapping experiments revealed that the key active species like O2 •-, •OH, and h+ can exist and play an important role in methylene blue photodegradation.

Reduced graphene oxide-decorated CdS/ZnO nanocomposites for photoreduction of hexavalent chromium and photodegradation of methylene blue.

CdS/ZnO/rGO, ZnO/CdS, and ZnO/rGO hetero-nanocomposites were successfully prepared by the facile one-pot solvothermal method. CdI2(benztsczH)2 (where benztsczH = benzaldehyde thiosemicarbazone) for CdS and zinc acetate dihydrate for ZnO synthesis were used as single-source precursors (SSP) in the presence of two-dimensional graphene oxide. The obtained nanocomposites were well characterized using spectroscopic techniques. An ultrafast catalytic activity is observed for the photoreduction of toxic hexavalent to non-toxic trivalent chromium using ternary tandem CdS/ZnO/rGO in comparison with binary ZnO/CdS and ZnO/rGO. The reduced graphene oxide-decorated CdS/ZnO nanocomposites show complete photoreduction of Cr(VI) to Cr(III) in 2 minutes. It is the shortest time frame for the reduction of toxic chromium without the use of noble metals like Pt, Pd, and Au. The complete photodegradation of MB was also achieved by the ternary nanocomposite in 50 minutes. The plausible mechanisms for harvesting sunlight by the binary and ternary nanocomposites are suggested by the valence and conduction band potential values and Mulliken electronegativity of individual cations. Experiments were also carried out using scavengers to strongly support the mechanism by showing the responsible reactive species involved in the MB dye photodegradation.

Single-Step Production of a TiO2@MoS2 Heterostructure and Its Applications as a Supercapacitor Electrode and Photocatalyst for Reduction of Cr(VI) to Cr(III).

In this study, we have reported a one-step synthesis of a TiO2@MoS2 heterostructure. TiO2@MoS2 was synthesized using a facile and cost-effective method. The as-synthesized TiO2@MoS2 heterostructure was characterized by suitable spectroscopic techniques. The obtained TiO2@MoS2 was utilized as a supercapacitor electrode material. Electrochemical studies show that the TiO2@MoS2 heterostructure possesses a specific capacitance of 337 F/g at a current density of 1 A/g in an aqueous solution. Furthermore, an application as a photocatalyst for the photoreduction of toxic hexavalent chromium was reported for the first time. This heterostructure showed the photoreduction of Cr6+ to Cr3+ in 120 min with formic acid as a scavenger under direct sunlight. A plausible mechanism of photoreduction of Cr6+ to Cr3+ under natural sunlight irradiation using TiO2@MoS2 is proposed.

Single step, bulk synthesis of engineered MoS2 quantum dots for multifunctional electrocatalysis.

Bi- or tri- functional catalysts based on atomic layers are receiving tremendous scientific attention due to their importance in various energy technologies. Recent studies on molybdenum disulphide (MoS2) nanosheets revealed that controlling the edge states and doping/modifying with suitable elements are highly important in tuning the catalytic activities of MoS2. Here we report a bulk, single step method to synthesize metal modified MoS2 quantum dots (QDs). Three elements, namely Fe, Mg and Li, are chosen to study the effects of dopants in the catalytic activities of MoS2. Fe and Mg are found to act like dopants in the MoS2 lattice forming respective doped MoS2 QDs, while Li formed an intercalated MoS2 QD. The efficacy and tunability of these luminescent doped QDs towards various electrocatalytic activities (hydrogen evolution reaction, oxygen evolution reaction and oxygen reduction action) are reported here.