Enhanced photocatalytic performance of ZnO under visible light by co-doping of Ta and C using hydrothermal method.

This study attempted to improve the photocatalytic activity of zinc oxide (ZnO) semiconductors in the visible light region by introducing the co-doping of carbon (C) and tantalum (Ta) to ZnO (ZTC) using a simple hydrothermal method with the respective precursors. The obtained uniform ZTC nanoparticles with an average crystal size of 29.30 nm (according to Scherrer's equation) revealed a redshift with a decrease in bandgap (Eg) from 3.04 eV to 2.88 eV, allowing the obtained photocatalyst to absorb the energy of the visible light for photocatalysis. Furthermore, the Zn 2p and Ta 4f core level spectra confirmed the presence of Zn2+ and Ta5+ in the ZTC sample. In addition, the infrared spectra identified hydrogen-related defects (HRDs), while the O 1s spectra indicated the existence of oxygen vacancies (VO). Electrochemical tests revealed improvement in the electron conductivity and charge separation of the obtained materials. To follow, the photocatalytic performance assessment was conducted by varying the C/Zn2+ ratios (5, 10, and 15 mol%) in ZTC samples, the initial RhB concentration (7, 15, and 30 ppm), and the pH of the RhB solution (3.0-10.0). The photodegradation on ZTC samples showed the most effectiveness for a 7 ppm RhB solution with a C/Zn2+ ratio of 10 mol% in the slightly alkaline medium (pH 9.0). Additionally, ZTC also exhibited commendable durability after being reused several times. The nature of RhB photodegradation was proposed and discussed via a mechanism at the end of this work.

Microplastics and trace metals in river sediment: Prevalence and correlation with multiple factors.

Microplastics (MPs), which are ubiquitous, are no longer novel emerging pollutants, yet our knowledge of them is insufficient. This study investigates the prevalence of MPs and trace metals in sediment belonging to Ma River, Vietnam, and their interaction with various parameters, including nutrients such as total carbon (TC), total nitrogen (TN), and total phosphorus (TP), grain sizes, and MPs in surface water. The study revealed that the abundance of MPs in sediment (MPs/S) is relatively high (i.e., 1328.3 ± 1925.5 items.kg-1 dry weight), while the concentration of MPs in surface water (MPs/W) was relatively low (i.e., 57.3 ± 55.8 items.m-3) compared to other areas. Notably, the study found that arsenic and cadmium concentrations exceeded baseline levels, indicating their anthropogenic origin. To interpret the relationship between MPs/S, metals, and the aforementioned parameters, principal component analysis and Pearson correlation analyses were employed. The results demonstrated a significant correlation between metals and nutrients, as well as small grain sizes such as clay and silt. It was observed that the majority of metals displayed co-occurrence with one another but showed weak associations with the levels of MPs present in both water and sediment. Additionally, a weak correlation was observed between MPs/W and MPs/S. In conclusion, these findings suggest that the distribution and behavior of MPs and trace metals in aquatic systems are influenced by multiple factors, including nutrient levels, grain size, and other chemical and physical characteristics of the environment. While certain metals may have natural sources, others may result from human activities such as mining, industrial discharge, and wastewater treatment plants. As a result, understanding the sources and aspects of metal contamination are critical for determining their relationship with MPs and developing effective strategies for mitigating their impact on aquatic ecosystems.

One-step hydrothermal preparation of Ta-doped ZnO nanorods for improving decolorization efficiency under visible light.

In this work, Ta-doped ZnO (Ta-ZnO) nanomaterials were synthesized by the hydrothermal method at different temperatures (110, 150, and 170 °C) for the photodegradation of methylene blue (MB) under visible light. Ta doping significantly affects the crystal defects, optical properties, and MB photocatalytic efficiency of ZnO materials. The optical absorption edge of Ta-ZnO 150 was redshifted compared to undoped ZnO, correlating to bandgap narrowing (E gTa-ZnO = 2.92 eV; E gZnO = 3.07 eV), implying that Ta doped ZnO is capable of absorbing visible light. Besides, Ta-doping was the reason for enhanced blue light emission in the photoluminescence spectrum, which is related to the oxygen defect V 0 O. It is also observed in the XPS spectra, where the percentage of oxygen in the oxygen-deficient regions (O531.5 eV) of Ta-ZnO150 is higher than that of ZnO150. It is an important factor in enhancing ZnO's photocatalytic efficiency. The MB degradation efficiency of Ta-doped ZnO reached the highest for Ta-ZnO 150 and was 2.5 times higher than ZnO under a halogen lamp (HL). Notably, the influence of hydrothermal temperature on the structural, morphological, and photoelectrochemical properties was discussed in detail. As a result, the optimal hydrothermal temperature for synthesizing the nanorod is 150 °C. Furthermore, photocatalytic experiments were also performed under simulated sunlight and natural sunlight. The nature of the photo-oxidative degradation of MB was also investigated.

Facile construction of S-scheme SnO2/g-C3N4 photocatalyst for improved photoactivity.

The SnO2/g-C3N4 composites were fabricated via an annealing mixture of g-C3N4 and SnO2, which were obtained from calcinating melamine and hydrothermal treatment of SnCl4 solution, respectively. The photocatalytic properties of g-C3N4/SnO2 were studied over the degradation of Rhodamine B (RhB) under visible light, which exhibits a significantly improved photocatalytic activity compared to the single components, g-C3N4 and SnO2. The enhancement in photocatalytic activity of SnO2/g-C3N4 could be described by the S-scheme pathway, in which the effective charge transfer between components is demonstrated toward the suppression in recombination of the photogenerated electron-hole pairs within redox potential conservation. Besides, a new criterion, photochemical space-time yield, was applied to evaluate the photocatalytic performance of our samples.

A comparative study of 0D and 1D Ce-ZnO nanocatalysts in photocatalytic decomposition of organic pollutants.

Nanosized zinc oxide is an intriguing material that can be applied in various fields. In this study, Ce doped ZnO nano-catalysts (Ce-ZnO) were synthesized by two different methods (i.e., hydrothermal (Ce-ZnO-HT) and polymer gel combustion (Ce-ZnO-CB) methods) to compare their photodegradation efficiency. The prepared material characteristics were investigated using XRD, SEM, TEM, FTIR, UV-Vis, PL, XPS, EDS, and BET. The bandgap of both nanoparticles (NPs) was 2.95 eV, despite the fact that the morphology of Ce-ZnO-HT NPs was 1D-rod-shaped and that of Ce-ZnO-CB NPs was 0D-spherical. However, the surface area and oxygen vacancy rate of Ce-ZnO-HT NPs were higher than those of Ce-ZnO-CB NPs. These differences are directly related to the photocatalytic activity of Ce-ZnO NPs. Accordingly, the results showed that photocatalytic efficiency was classified in the order Ce-ZnO-HT > Ce-ZnO-CB > pure ZnO, and the photocatalytic reaction rate constant of Ce-ZnO-HT used to decompose MB was 3.0 times higher than that of Ce-ZnO-CB. Interestingly, the photodegradation mechanism study revealed that hydroxyl radicals and holes were shown to be more important contributors to methyl blue degradation than photo-induced electrons and superoxide radical ions.