Enhanced sono-dispersion of Bi5O7I and Bi2ClHO3 oxides over ZnO used as nanophotocatalyst in solar-light-driven removal of methylene blue from water

Enhanced mitigation of acidic and basic dyes by ZnO based nano-photocatalysis: current applications and future perspectives

Dye wastewater possess immense toxicity with carcinogenic properties and they persist in environment owing to their stability and resistance to chemical and photochemical changes. The bio degradability of dye-contaminated wastewater is low due to its complex molecular structure. Nano-photocatalysts based on zinc oxide are reported as one of the effective metal oxides for dye remediation due to their photostability, enhanced UV and visible absorption capabilities in an affordable manner. An electron-hole pair forms when electrons in the valence band of ZnO nano-photocatalyst transfer into the conduction band by absorbing UV light. The review article presents a detailed review on ZnO applications for treating acidic and basic dyes along with the dye degradation performance based on operating conditions and photocatalytic kinetic models. Several acidic and basic dyes have been shown to degrade efficiently using ZnO and its nanocomposites. Higher removal percentages for crystal violet was reported at pH 12 by ZnO/Graphene oxide catalyst under 400 nm UV light, whereas acidic dye Rhodamine B at a pH of 5.8 was degraded to 100% by pristine ZnO. The mechanism of action of ZnO nanocatalysts in degrading the dye contamination are reported and the research gaps to make these agents in environmental remediation on real time operations are discussed.

Visible-light-driven photodegradation of methylene blue and doxycycline hydrochloride by waste-based S-scheme heterojunction photocatalyst Bi5O7I/PCN/tea waste biochar

Herein, we have reported a photocatalytic Bi5O7I, protonated g-C3N4 heterojunction with directional charge transfer channels provided by tea waste biochar to achieve effective e-/h+ pair isolation for the improved degradation of Methylene blue (MB) and Doxycycline hydrochloride (DCHCl). An S-scheme heterojunction was fabricated via the novel method that combined hydrothermal and ultrasonic dispersion, followed by an electrostatic self-assembly route. The as-fabricated Bi5O7I/protonated g-C3N4/Tea waste biochar heterojunction formed a strong contact at the interface, as supported by the electron microscopic results. As per the adsorption and photocatalytic degradation kinetics study, Bi5O7I/Tea waste biochar/protonated g-C3N4 (40 wt%) heterojunction showed a higher adsorption rate of 41.56% and 32% for MB and DCHCl within 30 min in the dark. Also, 92.02% MB and 90.21% DCHCl degradation rates in 60 and 90 min, respectively, are approximately 43 and 32 times higher than bare Bi5O7I and protonated g-C3N4 photocatalysts. The highest adsorption and degradation rate was achieved owing to the addition of Tea waste biochar and protonated g-C3N4 in a controlled ratio, and the sufficient interfacial contact between Bi5O7I and protonated g-C3N4 is for the improved isolation rate of e-/h+ pairs as evidenced by zeta potential values photoluminescence spectra as well as from scanning and transmission electron microscopy. Moreover, Bi5O7I/Tea waste biochar/protonated g-C3N4 (40 wt%) possessed high stability and recyclability after four consecutive cycles without much altering the degradation ability. Therefore, we believe that the as-fabricated Bi5O7I/Tea waste biochar/protonated g-C3N4 (40 wt%) provides new insight into the highly efficient S-scheme mechanisms significant for accelerating multicomponent photocatalytic redox reactions; while forming an effective visible light responsive candidate for treating wastewater.

Evaluation of global research trends in photocatalytic degradation of dye effluents using scientometrics analysis

Photocatalysis technology is observed to be an effective approach for its outstanding performance to eliminate wide range of organic pollutants including dyes in textile effluent. Despite growing number of studies, there is no scientometric perspective addressing the research topic "photocatalytic degradation of dye effluents". In this regard, a total of 954 documents were extracted from the Web of Science (WoS) database using keywords search to cover all the published documents during the period 1996-2020. Publications in this area started to increase exponentially from year 2007. The most dominant subject categories were Engineering, Chemistry and Environmental Science & Ecology. Applied Catalysis B-Environmental and Desalination & Water Treatment were identified as the most-impactful and productive journals respectively. Authors based in India accounted for 29.6% of total publications followed by China (14.2%); but in terms of citations Spain and Italy were more influential. Based on keyword analysis, azo dyes, TiO2, nanoparticles, adsorption, methylene blue, visible light, ZnO and kinetics are the most studied, and visible light mediated photocatalysis, hybrid treatment systems, nano based photocatalysis and more recently, metal based photocatalysis, have received most attention. Studies on cost and energy analysis, recovery of value-added products, development of more efficient photocatalytic materials and new photocatalyst regeneration approaches should be considered for future research. This study therefore, provides a comprehensive understanding about the trends and patterns of the specified research field worldwide.

Elimination of rhodamine B from textile wastewater using nanoparticle photocatalysts: A review for sustainable approaches

Rhodamine B (RhB) dye used in the textile industries is associated with carcinogenic and neurotoxic effects with a high potential to cause a variety of human diseases. Semiconductor photocatalysts synthesised through agriculture waste extracts exhibited high efficiency for RhB removal. The current review aimed to explore the efficiency and mechanism of RhB degradation using different photocatalysts that have been used in recent years, as well as the effect of various factors on the removal process. Zinc oxide nanoparticles (ZnO NPs) synthesised from plant extract is the most effective for the RhB degradation with the efficiency reaching 100% after 210 min. The photocatalysis process depends on the pH because pH changes the balance of water dissociation, which impacts the formation of hydroxyl radicals and the surface load of the catalyst. Analysis using Jupyter Notebook revealed a strong correlation between the concentration of ZnO NPs and the photocatalysis efficiency (R = 0.72). These findings reveal that man-sized photocatalysts have a high potential for removing RhB from the wastewater.

Enhanced heterogeneous catalytic ozonation of pharmaceutical pollutants using a novel nanostructure of iron-based mineral prepared via plasma technology: A comparative study

Plasma-treated goethite nanoparticles with high surface area and improved density of surface hydroxyl groups were synthesized from natural goethite (NG) using Argon (PTG-Ar) and Nitrogen (PTG-N₂) as plasma environment to enhance the performance of heterogeneous catalytic ozonation process. Synthesized samples were characterized by FESEM, EDX, TEM, XRD, XPS, BET-BJH, FTIR, AAS and pH_PZC. Results indicated a significantly different morphology for the prepared samples with negligible change in crystal structure. Furthermore, the catalytic activity and synergy factor of the NG and PTG nanocatalysts were evaluated for degradation and mineralization of Sulfasalazine antibiotic (SSZ) as an environmental hazardous contaminant. The highest removal efficiency was achieved 96.05 % under the optimal operating conditions. The kinetic study confirmed the pseudo-first-order reaction for the degradation process. Moreover, the dissolved ozone concentration and effect of organic and inorganic salts were studied in order to assess the reactive oxidant species (ROSs) and catalyst active sites in the process. The mechanism investigation showed the catalytic ozonation of SSZ was mainly performed by successive attacks of hydroxyl radicals (•OH), superoxide radicals (O₂^-) and direct ozone molecules. Environmentally-friendly modification of the NG, negligible iron leaching, successive reusability and superior catalytic activity are the major benefits of the PTG nanoparticles.