Highlighting unique function of immobilized superoxide on TiO2 for selective photocatalytic degradation

Prospects of TiO2-based photocatalytic degradation of microplastic leachates related disposable facemask, a major COVID-19 waste

COVID-19 is one of the serious catastrophes that have a substantial influence on human health and the environment. Diverse preventive actions were implemented globally to limit its spread and transmission. Personnel protective equipment (PPE) was an important part of these control approaches. But unfortunately, these types of PPE mainly comprise plastics, which sparked challenges in the management of plastic waste. Disposable face masks (DFM) are one of the efficient strategies used across the world to ward off disease transmission. DFMs can contribute to micro and nano plastic pollution as the plastic present in the mask may degrade when exposed to certain environmental conditions. Microplastics (MPs) can enter the food chain and devastate human health. Recognizing the possible environmental risks associated with the inappropriate disposal of masks, it is crucial to avert it from becoming the next plastic crisis. To address this environmental threat, titanium dioxide (TiO2)-based photocatalytic degradation (PCD) of MPs is one of the promising approaches. TiO2-based photocatalysts exhibit excellent plastic degradation potential due to their outstanding photocatalytic ability, cost efficiency, chemical, and thermal stability. In this review, we have discussed the reports on COVID-19 waste generation, the limitation of current waste management techniques, and the environmental impact of MPs leachates from DFMs. Mainly, the prominence of TiO2 in the PCD and the applications of TiO2-based photocatalysts in MPs degradation are the prime highlights of this review. Additionally, various synthesis methods to enhance the photocatalytic performance of TiO2 and the mechanism of PCD are also discussed. Furthermore, current challenges and the future research perspective on the improvement of this approach have been proposed.

Adsorption-enhanced photocatalytic property of Ag-doped biochar/g-C3N4/TiO2 composite by incorporating cotton-based biochar

In this study, the biochar obtained from waste cotton fibers was introduced into the Ag-doped g-C3N4/TiO2 hybrid composite through a facile one-step hydrothermal process. The morphology, elemental composition, crystal structure, microstructure, specific surface area, chemical bonding state, energy band structure, and separation efficiency of photoinduced charge carriers of the resultant composite were examined using scanning electron microscope, energy dispersive X-ray spectrometer, X-ray diffractometer, transmission electron microscope, surface area analyzer, X-ray photoelectron spectroscope, Ultraviolet-visible spectrophotometer, ultraviolet photoelectron spectroscope, and photoluminescence spectroscope. The adsorption isotherms, kinetics and thermodynamics of the biochar, Ag-doped g-C3N4/TiO2 and Ag-doped biochar/g-C3N4/TiO2 were evaluated using the model methyl orange dye. The photoacatalytic degradation of the model pollutants including methyl orange, methylene blue, congo red, and tetracycline hydrochloride and the photocatalytic reduction of Cr(VI) ions were also assessed under visible light. Experimental results indicated that the photocatalytic property of the Ag-doped biochar/g-C3N4/TiO2 was significantly enhanced through the adsorption enhancement compared with the Ag-doped g-C3N4/TiO2. This was due to the uniform doping of multi-scale porous biochar with g-C3N4 nanosheet, Ag and TiO2 nanoparticles. The adsorptive enhancement induced by the biochar resulted in the narrowed band gap, suitable electronic energy band structure, and fast separation of photoinduced charge carriers of the Ag-doped biochar/g-C3N4/TiO2, which was probably due to the coexistence of multi-valence Ti+4/+3 and Ag0/+1 species and oxygen-containing groups of biochar. The major reactive species of the Ag-doped biochar/g-C3N4/TiO2 were 1O2 and h+. The MO dye adsorption onto the Ag-doped biochar/g-C3N4/TiO2 followed the Langmuir isotherm model, pseudo-first-order and pseudo-second-order kinetic models, and the adsorption process was an endothermic reaction with entropy reduction effects. As such, the Ag-doped biochar/g-C3N4/TiO2 exhibited a promising application for the treatment of wastewater containing multi-pollutants especially organic dyes and heavy metal ions.

Modification of naturally abundant resources for remediation of potentially toxic elements: A review

Water and soil contamination due to potentially toxic elements (PTEs) represents a critical threat to the global ecosystem and human health. Naturally abundant resources have significant advantages as adsorbent materials for environmental remediation over manufactured materials such as nanostructured materials and activated carbons. These advantages include cost-effectiveness, eco-friendliness, sustainability, and nontoxicity. In this review, we firstly compare the characteristics of representative adsorbent materials including bentonite, zeolite, biochar, biomass, and effective modification methods that are frequently used to enhance their adsorption capacity and kinetics. Following this, the adsorption pathways and sites are outlined at an atomic level, and an in-depth understanding of the structure-property relationships are provided based on surface functional groups. Finally, the challenges and perspectives of some emerging naturally abundant resources such as lignite are examined. Although both unamended and modified naturally abundant resources face challenges associated with their adsorption performance, cost performance, energy consumption, and secondary pollution, these can be tackled by using advanced techniques such as tailored modification, formulated mixing and reorganization of these materials. Recent studies on adsorbent materials provide a strong foundation for the remediation of PTEs in soil and water. We speculate that the pursuit of effective modification strategies will generate remediation processes of PTEs better suited to a wider variety of practical application conditions.