Synthesis, characterization and photocatalytic application of TiO2 /magnetic graphene for efficient photodegradation of crystal violet

Molecular surface-dependent light harvesting and photo charge separation in plant-derived carbon quantum dots for visible-light-driven OH radical generation for remediation of aromatic hydrocarbon pollutants and real wastewater

Despite the growing emphasis on eco-friendly nanomaterials as energy harvesters, scientists are actively searching for metal-free photocatalysts to be used in environmental remediation strategies. Developing renewable resource-based carbon quantum dots (CQDs) as the sole photocatalyst to harvest visible light for efficient pollutant degradation is crucial yet challenging, particularly for addressing the escalating issue of water deterioration. Moreover, the photocatalytic decomposition of H2O2 under visible light irradiation remains an arduous task. Based on this, we designed two types of CQDs, C-CQDs (carboxylic-rich) and A-CQDs (amine-rich) with distinct molecular surfaces. Owing to the higher amount of upward band bending induced by amine-rich molecular surface, A-CQDs efficiently harvest the visible light and prevent recombination kinetics resulting in prolonged lifetimes (25 ps), and augmented charge carrier density (35.7 × 1018) of photoexcited charge carriers. A-CQDs enabled rapid visible-light-driven photolysis of H2O2 (k = 0.058 min-1) and produced higher quantity of •OH radicals (0.158 μmol/sec) for the mineralization of petroleum waste, BETX (i.e. Benzene, Ethylbenzene, Toluene and Xylene) (k = 0.017-0.026 min-1) and real textile wastewater (k = 0.026 min-1). To assess comparative toxicities of both remediated and non-remediated real wastewater samples in a time and dose depended manner, Drosophila melanogaster was used as a model organism. The findings unequivocally demonstrate the potential of remediated wastewater for watering urban forestry.

Ternary Graphene Oxide and Titania Nanoparticles-Based Nanocomposites for Dye Photocatalytic Degradation: A Review

Advanced oxidation processes stand as green alternatives for the decontamination of waste waters. Photocatalysis is an advanced oxidation process in which a semiconductor material absorbs photon energy and triggers redox reactions capable of degrading organic pollutants. Titanium dioxide (TiO2, titania) represents one of the most popular choices of photocatalytic materials, however the UV-activation of its anatase phase and its high charge recombination rate decrease its photocatalytic activity and weaken its potential. Graphene oxide is a 2D carbon nanomaterial consisting of exfoliated sheets of hexagonally arranged carbons decorated with oxygen- and hydrogen- functional groups. Composite nanomaterials consisting of titania nanoparticles and graphene oxide have proven to enhance the photocatalytic activity of pure TiO2. In this review, we present a thorough literature review of ternary nanocomposites based on synthesized or commercial titania nanoparticles and GO (or reduced GO) particularly used for the photodegradation of dyes. GO/TiO2 has been enriched primarily with metals, semiconductors and magnetic nanomaterials, proving a superior dye degradation performance and reusability compared to bare TiO2. Ongoing challenges and perspectives are outlined.

Highly Efficient Solar Light Driven g-C3N4@Cs0.33WO3 Heterojunction for the Photodegradation of Colorless Antibiotics

This study facilitates the synthesis of a graphitic carbon nitride/cesium tungsten oxide (g-C₃N₄@Cs_0.33WO₃) heterojunction using a solvothermal method. The photocatalytic activities of the prepared samples were examined for the photodegradation of colorless antibiotics, namely tetracycline, enrofloxacin, and ciprofloxacin, as well as cationic and anionic dyes, such as methyl orange, rhodamine B, neutral red, and methylene blue, under full-spectrum solar light. We have purposely selected different kinds of wastewater pollutants of colorless antibiotics and cationic and anionic organic dyes to investigate the potential application of this heterojunction toward different groups of water pollutants. The results revealed that the g-C₃N₄@Cs_0.33WO₃ heterojunction showed an outstanding photocatalytic activity toward all the pollutants with concentrations of 20 ppm each at pH 3 by photocatalytically removing 97% of tetracycline within 3 h, 98% of enrofloxacin within 2 h, 97% of ciprofloxacin within 2.25 h, 98% of methylene blue in 1 h, 99% of rhodamine B within 2 h, 99% of neutral red in 1.25 h, and 95% of methyl orange in 2 h. These findings indicate that the developed photocatalyst possesses excellent photocatalytic properties toward seven different water pollutants that make it a universal photocatalyst. The developed g-C₃N₄@Cs_0.33WO₃ oxide heterojunction also presented a photocatalytic performance better than those of reported solar light active photocatalysts for photodegradation of rhodamine B and tetracycline. The efficient photocatalytic performance of the heterojunction can be ascribed to its extended light-absorbing ability, effective charge separation and fast charge transfer properties, and a high surface area. Moreover, an active species detection experiment also confirmed that superoxide radicals, hydroxyl radicals, and holes played significant roles in the photocatalysis of the organic dyes and tetracycline.

Visible light photodegradation of organic dyes using electrochemically synthesized MoO3/ZnO

In this study, flake-like MoO₃-ZnO composite was prepared using a simple and robust electrochemical setup. The composite was characterized by X-ray diffraction, Fourier transform infrared spectroscopy, scanning electron microscopy, elemental analysis, X-ray photoelectron spectroscopy, thermogravimetric analysis, photoluminescence, zeta potential analysis, and electrochemical impedance study. The modified ZnO shows a remarkable catalytic activity towards the photodegradation of three potentially hazardous dyes, malachite green, crystal violet, and methylene blue. More than 95% of both malachite green and crystal violet degraded within 140 min under visible light irradiation. Scavenger studies reveal that OH· radicals produced by the photo-separated charges on MoO₃-ZnO are responsible for the degradation of all three dyes. The photoactive charge carriers show less recombination rate as evidenced by the photoluminescence spectrum due to the interparticle charge migration process. This work suggests a new versatile procedure for the synthesis of MoO₃-ZnO composites and establishes its photocatalytic efficacy under visible light with three common pollutant dyes found in wastewater.

Dynamic processes in conjunction with microbial response to disclose the biochar effect on pentachlorophenol degradation under both aerobic and anaerobic conditions

Organochlorines are critical soil contaminants and the use of biochar has recently shown potential to improve soil remediation. However, little is known about biochar-microbe interactions nor the impact on environmental processes such as the immobilization and biodegradation of organochlorine compounds. In this study, we performed microcosm experiments to elucidate how biochar affected the biodegradation and sequestration of pentachlorophenol (PCP). Our results showed that the amendment of biochar markedly inhibited PCP biodegradation due to a strong sorption affinity for PCP under both aerobic and anaerobic conditions. Notably, the inhibitory effect was relatively weaker under anaerobic conditions than under aerobic conditions. The addition of biochar can dramatically shift the bacterial community diversity in the PCP-spiked soils. Under aerobic conditions, biochar significantly stimulated the growth of PCP-degrading bacteria Bacillus and Sphingomonas, but reduced the opportunities for microbes to contact with PCP directly. Under anaerobic conditions, the non-strict organohalide-respiring bacteria Desulfovibrio, Anaeromyxobacter, Geobacter and Desulfomonile were the main drivers of PCP transformation. Our results imply that the use of biochar as a soil remediation strategy for organochlorine compounds should be cautious.

Photocatalytic decomposition of selected biologically active compounds in environmental waters using TiO2/polyaniline nanocomposites: Kinetics, toxicity and intermediates assessment

A comprehensive study of the removal of selected biologically active compounds (pharmaceuticals and pesticides) from different water types was conducted using bare TiO₂ nanoparticles and TiO₂/polyaniline (TP-50, TP-100, and TP-150) nanocomposite powders. In order to investigate how molecular structure of the substrate influences the rate of its removal, we compared degradation efficiency of the initial substrates and degree of mineralization for the active components of pharmaceuticals (propranolol, and amitriptyline) and pesticides (sulcotrione, and clomazone) in double distilled (DDW) and environmental waters. The results indicate that the efficiency of photocatalytic degradation of propranolol and amitriptyline was higher in environmental waters: rivers (Danube, Tisa, and Begej) and lakes (Moharač, and Sot) in comparison with DDW. On the contrary, degradation efficacy of sulcotrione and clomazone was lower in environmental waters. Further, of the all catalysts applied, bare TiO₂ and TP-100 were found to be most effective in the mineralization of propranolol and amitriptyline, respectively, while TP-150 appeared to be the most efficient in terms of sulcotrione and clomazone mineralization. Also, there was no significant toxicity observed after the irradiation of pharmaceuticals or pesticides solutions using appropriate catalysts on rat hepatoma (H-4-II-E), mouse neuroblastoma (Neuro-2a), human colon adenocarcinoma (HT-29), and human fetal lung (MRC-5) cell lines. Subsequently, detection and identification of the formed intermediates in the case of sulcotrione photocatalytic degradation using bare TiO₂ and TP-150 showed slightly different pathways of degradation. Furthermore, tentative pathways of sulcotrione photocatalytic degradation were proposed and discussed.