Non-high temperature method to synthesize carbon coated TiO2 nano-dendrites for enhanced wide spectrum photocatalytic hydrogen evolution activity

Kilogram-scale fabrication of TiO2 nanoparticles modified with carbon dots with enhanced visible-light photocatalytic activity

Incorrect discharge of dye wastewater will cause environment pollution and be very harmful to human health. Visible-light photocatalysis over large-scale synthesized semiconductor materials can become one of the feasible solutions for the practical application of purifying dye wastewater. As a new candidate, carbon dots (CDs) with unique fluorescence were fabricated on a tens of grams scale and then further applied to the kilogram-scale synthesis of a CDs/TiO₂ composite by one-step heat treatment. Compared with single TiO₂ nanoparticles (NPs), the CDs/TiO₂ composite with a large specific surface area exhibits enhanced photo-degradation performance for methyl orange (MO). This phenomenon can be attributed to the loading of CDs in the TiO₂ NPs, which is conducive to broadening the light absorption spectrum and improving absorption intensity, narrowing the band gap, charge carrier trapping, up-converting properties, and charge separation. The kilogram-scale synthesis of the CDs/TiO₂ photocatalyst does not affect the morphology, structure, optical properties and photocatalytic performance of the composite, which opens up a new avenue to construct elaborate heterostructures for enhanced photocatalytic performance using visible light as the light source.

ZnO Nanoparticles Modified by Carbon Quantum Dots for the Photocatalytic Removal of Synthetic Pigment Pollutants

Synthetic pigment pollutants caused by the rapid development of the modern food industry have become a serious threat to people's health and quality of life. Environmentally friendly ZnO-based photocatalytic degradation exhibits satisfactory efficiency, but some shortcomings of large band gap and rapid charge recombination reduce the removal of synthetic pigment pollutants. Here, carbon quantum dots (CQDs) with unique up-conversion luminescence were applied to decorate ZnO nanoparticles to effectively construct the CQDs/ZnO composites via a facile and efficient route. The ZnO nanoparticles with a spherical-like shape obtained from a zinc-based metal organic framework (zeolitic imidazolate framework-8, ZIF-8) were coated by uniformly dispersive quantum dots. Compared with single ZnO particles, the obtained CQDs/ZnO composites exhibit enhanced light absorption capacity, decreased photoluminescence (PL) intensity, and improved visible-light degradation for rhodamine B (RhB) with the large apparent rate constant (k _app). The largest k _app value in the CQDs/ZnO composite obtained from 75 mg of ZnO nanoparticles and 12.5 mL of the CQDs solution (∼1 mg·mL^-1) was 2.6 times that in ZnO nanoparticles. This phenomenon may be attributed to the introduction of CQDs, leading to the narrowed band gap, an extended lifetime, and the charge separation. This work provides an economical and clean strategy to design visible-light-responsive ZnO-based photocatalysts, which is expected to be used for the removal of synthetic pigment pollutants in food industry.

Synergistic Effects of Fluorine and WO3 Nanoparticles on the Surface of TiO2 Hollow Spheres for Enhanced Photocatalytic Activity under Visible Light Irradiation

TiO₂ is an attractive catalyst for the photocatalytic degradation of organic pollutants. However, owing to its large band gap, it can only be activated by ultraviolet (UV) light, which constitutes a small portion of solar energy. Therefore, there has been significant interest in extending its light absorption range from UV to visible light. In this study, fluorinated TiO₂ hollow spheres (FTHSs) were prepared via a rapid and simple wet chemical process using ammonium hexafluorotitanate, and then FTHS/WO₃ heterostructures with different weight ratios of the FTHS and WO₃ nanoparticles were synthesized via a simple wet impregnation method. The formation of the hybrid structure was confirmed by various characterization techniques. The photocatalytic activity of the synthesized photocatalysts in the photodegradation of rhodamine B, a model pollutant, was evaluated under visible light irradiation. The FTHS/WO₃ heterostructures exhibited significantly improved photocatalytic activity compared to the bare FTHS or WO₃ nanoparticles. The photodegradation efficiency of the FTHS/WO₃ heterostructure in the present study was up to 0.0581 min^-1. Detailed mechanisms that lead to the enhanced photocatalytic activity of the heterostructures are discussed. In addition, comparative experiments reveal that the photodegradation efficiency of the FTHS/WO₃ heterostructure under visible light irradiation is superior to that of the P25/WO₃ heterostructure prepared from the commercially available TiO₂ catalyst (P25) via the same impregnation method.

Enhanced Photocatalytic Antibacterial Properties of TiO2 Nanospheres with Rutile/Anatase Heterophase Junctions and the Archival Paper Protection Application

TiO2 has been generally studied for photocatalytic sterilization, but its antibacterial activities are limited. Herein, TiO2 nanospheres with rutile/anatase heterophase junctions are prepared by a wet chemical/annealing method. The large BET surface area and pore size are beneficial for the absorption of bacteria. The rutile/anatase heterojunctions narrow the bandgap, which enhances light absorption. The rutile/anatase heterojunctions also efficiently promote the photogenerated carriers' separation, finally producing a high yield of radical oxygen species, such as •O2- and •OH, to sterilize bacteria. As a consequence, the obtained TiO2 nanospheres with rutile/anatase heterojunctions present an improved antibacterial performance against E. coli (98%) within 3 h of simulated solar light irradiation, exceeding that of TiO2 nanospheres without annealing (amorphous) and TiO2 nanospheres annealing at 350 and 550 °C (pure anatase). Furthermore, we design a photocatalytic antibacterial spray to protect the file paper. Our study reveals that the TiO2 nanospheres with rutile/anatase heterojunctions are a potential candidate for maintaining the durability of paper in the process of archival protection.

Ni2P QDs decorated in the multi-shelled CaTiO3 cube for creating inter-shelled channel active sites to boost photocatalytic performance

Control and insight into the abundance of inter-shelled channel active sites and charge transport mechanism are the long-term challenges for enhancing photocatalytic activity. Herein, the Ni₂P quantum dots (QDs) are decorated in the multi-shelled CaTiO₃ cube for creating the abundance of inter-shelled channel active sites, which greatly improve the photocatalytic performances for generating H₂ and degrading tetracycline (TC) relative to pure CaTiO₃ and Ni₂P. Moreover, the Z-scheme mechanism and the quantum effect of the Ni₂P in multi-shelled CaTiO₃ cube play a crucial role for enhancing photocatalytic performance. Furthermore, the photoelectric researches demonstrate that the Ni₂P/CaTiO₃ heterostructure possesses more abundant active sites, smaller interface transmission resistance and faster photo-generated charge transfer efficiency. This work provides a meaningful model to research other materials with creating the abundance of inter-shelled channel active sites for the photo-electrocatalytic field.

Superior light absorbing CdS/vanadium sulphide nanowalls@TiO2 nanorod ternary heterojunction photoanodes for solar water splitting

Vanadium sulphide is an emerging infrared active photocatalyst that has not been utilized to its maximum potential.

Unveiling the enhanced photoelectrochemical and photocatalytic properties of reduced graphene oxide for photodegradation of methylene blue dye

Graphene oxide (GO) and reduced graphene oxide (rGO) can act as metal-free photocatalysts to remove aqueous dye pollutants under light illumination. However, there is some disparity in past reports on the origin of the photoactivity of GO and rGO for photodegradation of dye pollutants. In this work, the photoactivity of GO and rGO for methylene blue (MB) dye photodegradation were investigated with photoelectrochemical (PEC) measurements. The optimized rGO sample (G-2) exhibited a stable photocatalytic rate, which was 2.5 times higher than that of pure GO. PEC measurements revealed that the photocatalytic activity of G-2 was elevated due to higher photocurrent density, higher charge carrier density, and better charge separation. The changes in band gap and band positions of rGO were determined through optical characterization and Mott–Schottky (M–S) plots. Finally, the photocatalytic degradation mechanism of GO and rGO on MB dye was determined.

Photoactivity of graphene oxide (GO) was enhanced after reduction, this is due to improved photoelectrochemical properties.