Chhabilal Regmi

Fabrication of Ag-decorated BiOBr-mBiVO4 dual heterojunction composite with enhanced visible light photocatalytic performance for degradation of malachite green

A visible light active Ag-decorated BiVO4-BiOBr dual heterojunction photocatalyst was prepared using a facile hydrothermal method, followed by the photodeposition of Ag. The photocatalytic activity of the synthesized samples was investigated by monitoring the change in malachite green (MG) concentration upon visible light irradiation. The synthesized sample was highly effective for the degradation of non-biodegradable MG. The enhanced activity observed was ascribed to the efficient separation and transfer of charge carriers across the dual heterojunction structure as verified by photoluminescence measurements. The removal of MG was primarily initiated by hydroxyl radicals and holes based on scavengers effect. To gain insight into the degradation mechanism, both high performance liquid chromatography and high resolution-quantitative time of flight, electrospray ionization mass spectrometry measurements during the degradation process were carried out. The degradation primarily followed the hydroxylation and N-demethylation process. A possible reaction pathway is proposed on the basis of all the information obtained under various experimental conditions.

Understanding Mechanism of Photocatalytic Microbial Decontamination of Environmental Wastewater

Several photocatalytic nanoparticles are synthesized and studied for potential application for the degradation of organic and biological wastes. Although these materials degrade organic compounds by advance oxidation process, the exact mechanisms of microbial decontamination remains partially known. Understanding the real mechanisms of these materials for microbial cell death and growth inhibition helps to fabricate more efficient semiconductor photocatalyst for large-scale decontamination of environmental wastewater or industries and hospitals/biomedical labs generating highly pathogenic bacteria and toxic molecules containing liquid waste by designing a reactor. Recent studies on microbial decontamination by photocatalytic nanoparticles and their possible mechanisms of action is highlighted with examples in this mini review.

Microwave hydrothermal synthesis and upconversion properties of Yb3+/Er3+ doped YVO4 nanoparticles

Yb3+ and Er3+ doped YVO4 (Yb3+/Er3+:YVO4) nanoparticles with highly efficient near-infrared to visible upconversion properties have been synthesized by microwave hydrothermal process. Uniform-sized Yb3+/Er3+:YVO4 nanoparticles were synthesized within 1 h at 140 °C which is relatively faster than the conventional hydrothermal process. Under 980 nm laser excitation, strong green and less strong red emissions are observed which are attributed to 2H11/2, 4S3/2 to 4I15/2 and 4F9/2 to 4I15/2 transitions of Er3+ respectively. The emission intensity is found to depend strongly on the concentration of Yb3+. The quadratic dependence of upconversion intensity on the excitation power indicates that the upconversion process is governed by two-photon absorption process.

Cerium-doped β-Ni(OH)2 hexagon nanosheets: an effective photocatalyst for the degradation of the emerging water pollutant, naproxen

Nickel hydroxide β-Ni(OH)2 hexagonal nanosheets were synthetized via a hydrothermal exfoliation process. The practical microwave-assisted hydrothermal method facilitated obtaining layered nickel 3D nanoplates with cerium functionalization in 5 h. The as-produced nanostructures were characterized by XRD, XPS, FESEM, FTIR, PL, UV-vis, and BET techniques. The hydroxilated structures are nano-thick hexagonal plates with sides 28 nm in length and an average thickness of 5 nm. UV and PL irradiation was used to study the photoactive properties in the degradation of a pharmaceutical emerging pollutant, naproxen. UV-vis spectroscopy and high-performance liquid chromatography monitoring indicated that the Ni(OH)2-Ce nanostructures are an effective photocatalyst for naproxen degradation, including 40% mineralization of this highly recalcitrant drug. The photocatalyst showed stability for two consecutive cycles, preserving its photoactive and structural characteristics. Ce3+-doped nanoplates and surface functionalized Ce4+ act as charge separators and scavenging agents for the enhanced photodegradation of naproxen.