Adsorption and Photodegradation Efficiency of TiO2/Fe2O3/PAC and TiO2/Fe2O3/Zeolite Nanophotocatalysts for the Removal of Cyanide

Atrazine degradation through a heterogeneous dual-effect process using Fe-TiO2-allophane catalysts under sunlight

This study investigated the novel application of Fe-TiO2-allophane catalysts with 6.0 % w/w of iron oxide and two TiO2 proportions (10 % and 30 % w/w) for degrading atrazine (ATZ) using the heterogeneous dual-effect (HDE) process under sunlight. Comparative analyses with Fe-allophane and TiO2-allophane catalysts were conducted in both photocatalysis (PC) and HDE processes. FTIR spectra reveal the unique hydrous feldspathoids structure of allophane, showing evidence of new bond formation between Si-O groups of allophane clays and iron hydroxyl species, as well as Si-O-Ti bonds that intensified with higher TiO2 content. The catalysts exhibited an anatase structure. In Fe-TiO2-allophane catalysts, iron oxide was incorporated through the substitution of Ti4+ by Fe3+ in the anatase crystal lattice and precipitation on the surface of allophane clays, forming small iron oxide particles. Allophane clays reduced the agglomeration and particle size of TiO2, resulting in an enhanced specific surface area and pore volume for all catalysts. Iron oxide incorporation decreased the band gap, broadening the photoresponse to visible light. In the PC process, TiO2-allophane achieves 90 % ATZ degradation, attributed to radical species from the UV component of sunlight. In the HDE process, Fe-TiO2-allophane catalysts exhibit synergistic effects, particularly with 30 % w/w TiO2, achieving 100 % ATZ degradation and 85 % COD removal, with shorter reaction time as TiO2 percentage increased. The HDE process was performed under less acidic conditions, achieving complete ATZ degradation after 6 h without iron leaching. Consequently, Fe-TiO2-allophane catalysts are proposed as a promising alternative for degrading emerging pollutants under environmentally friendly conditions.

Statistical computational optimization approach for photocatalytic-ozonation decontamination of metronidazole in aqueous media using CuFe2O4/SiO2/ZnO nanocomposite

The increasing use of pharmaceuticals and the ongoing release of drug residues into the environment have resulted in significant threats to environmental sustainability and water safety. In this sense, developing a robust and easy-recovered magnetic nanocomposite with eminent photocatalytic activity is very imperative for detoxifying pharmaceutical compounds. Herein, a systematic study was conducted to investigate the photocatalytic ozonation for eliminating metronidazole (MET) from aqueous media utilizing the CuFe2O4/SiO2/ZnO heterojunction under simulated sunlight irradiation. The composite material was fabricated by a facile hydrothermal method and diagnosed by multiple advanced analytical techniques. Modelling and optimization of MET decontamination by adopting the central composite design (CCD) revealed that 90 % of MET decontamination can be achieved within 120 min of operating time at the optimized circumstance (photocatalyst dose: 1.17 g/L, MET dose: 33.20 mg/L, ozone concentration: 3.99 mg/min and pH: 8.99). In an attempt to scrutinize the practical application of the CuFe2O4/SiO2/ZnO/xenon/O3 system, roughly 56.18% TOC and 73% COD were removed under the optimized operational circumstances during 120 min of degradation time. According to the radical quenching experiments, hydroxyl radicals (HO•) were the major oxidative species responsible for the elimination of MET. The MET degradation rate maintained at 83% after seven consecutive runs, manifesting the efficiency of CuFe2O4/SiO2/ZnO material in the MET removal. Ultimately, the photocatalytic ozonation mechanism over the CuFe2O4/SiO2/ZnO heterojunction of the fabricated nanocomposites was rationally proposed for MET elimination. In extension, the results drawn in this work indicate that integrating photocatalyst and ozonation processes by the CuFe2O4/SiO2/ZnO material can be applied as an efficient and promising method to eliminate tenacious and non-biodegradable contaminants from aqueous environments.

Management of tannery waste effluents towards the reclamation of clean water using an integrated membrane system: A state-of-the-art review

Tanning and other leather processing methods utilize a large amount of freshwater, dyes, chemicals, and salts and produce toxic waste, raising questions regarding their environmental sensitivity and eco-friendly nature. Total suspended solids, total dissolved solids, chemical oxygen demand, and ions such as chromium, sulfate, and chloride turn tannery wastewater exceedingly toxic for any living species. Therefore, it is imperative to treat tannery effluent, and existing plants must be examined and upgraded to keep up with recent technological developments. Different conventional techniques to treat tannery wastewater have been reported based on their pollutant removal efficiencies, advantages, and disadvantages. Research on photo-assisted catalyst-enhanced deterioration has inferred that both homogeneous and heterogeneous catalysis can be established as green initiatives, the latter being more efficient at degrading organic pollutants. However, the scientific community experiences significant problems developing a feasible treatment technique owing to the long degradation times and low removal efficiency. Hence, there is a chance for an improved solution to the problem of treating tannery wastewater through the development of a hybrid technology that uses flocculation as the primary treatment, a unique integrated photo-catalyst in a precision-designed reactor as the secondary method, and finally, membrane-based tertiary treatment to recover the spent catalyst and reclaimable water. This review gives an understanding of the progressive advancement of a cutting-edge membrane-based system for the management of tanning industrial waste effluents towards the reclamation of clean water. Adaptable routes toward sludge disposal and the reviews on techno-economic assessments have been shown in detail, strengthening the scale-up confidence for implementing such innovative hybrid systems.

Effect of Doping TiO2 NPs with Lanthanides (La, Ce and Eu) on the Adsorption and Photodegradation of Cyanide-A Comparative Study

Free cyanide is a highly dangerous compound for health and the environment, so treatment of cyanide-contaminated water is extremely important. In the present study, TiO₂, La/TiO₂, Ce/TiO₂, and Eu/TiO₂ nanoparticles were synthesized to assess their ability to remove free cyanide from aqueous solutions. Nanoparticles synthesized through the sol-gel method were characterized by X-ray powder diffractometry (XRD), scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDS), Fourier-transformed infrared spectroscopy (FTIR), diffuse reflectance spectroscopy (DRS), and specific surface area (SSA). Langmuir and Freundlich isotherm models were utilized to fit the adsorption equilibrium experimental data, and pseudo-first-order, pseudo-second-order, and intraparticle diffusion models were used to fit the adsorption kinetics experimental data. Cyanide photodegradation and the effect of reactive oxygen species (ROS) on the photocatalytic process were investigated under simulated solar light. Finally, reuse of the nanoparticles in five consecutive treatment cycles was determined. The results showed that La/TiO₂ has the highest percentage of cyanide removal (98%), followed by Ce/TiO₂ (92%), Eu/TiO₂ (90%), and TiO₂ (88%). From these results, it is suggested that La, Ce, and Eu dopants can improve the properties of TiO₂ as well as its ability to remove cyanide species from aqueous solutions.

An Overview of Recent Developments in Improving the Photocatalytic Activity of TiO2-Based Materials for the Treatment of Indoor Air and Bacterial Inactivation

Indoor air quality has become a significant public health concern. The low cost and high efficiency of photocatalytic technology make it a natural choice for achieving deep air purification. Photocatalysis procedures have been widely investigated for environmental remediation, particularly for air treatment. Several semiconductors, such as TiO₂, have been used for photocatalytic purposes as catalysts, and they have earned a lot of interest in the last few years owing to their outstanding features. In this context, this review has collected and discussed recent studies on advances in improving the photocatalytic activity of TiO₂-based materials for indoor air treatment and bacterial inactivation. In addition, it has elucidated the properties of some widely used TiO₂-based catalysts and their advantages in the photocatalytic process as well as improved photocatalytic activity using doping and heterojunction techniques. Current publications about various combined catalysts have been summarized and reviewed to emphasize the significance of combining catalysts to increase air treatment efficiency. Besides, this paper summarized works that used these catalysts to remove volatile organic compounds (VOCs) and microorganisms. Moreover, the reaction mechanism has been described and summarized based on literature to comprehend further pollutant elimination and microorganism inactivation using photocatalysis. This review concludes with a general opinion and an outlook on potential future research topics, including viral disinfection and other hazardous gases.

Enhanced photocatalytic activity and charge carrier separation of CNT/TiO2/WO3/CdS catalyst for the visible-light photodegradation of reactive blue 19

The novel quaternary CNT/TiO₂/WO₃/CdS nanostructure was fabricated to be employed in the photocatalytic degradation of reactive blue 19 (RB19) under the visible light irradiation. The physicochemical properties of the pure TiO₂, CNT/TiO₂, CNT/TiO₂/WO₃, and CNT/TiO₂/WO₃/CdS were characterized using XRD, FTIR, FESEM, EDX, DRS, PL, and BET analyses. The photodegradation results showed that the optimum weight percentage of CNT, WO₃, and CdS was 4%, 35%, and 5%, respectively. The highest RB19 degradation efficiency of CNT/TiO₂/WO₃/CdS was achieved 97%. Besides, the central composite design was applied to model and optimize the photocatalytic activity of CNT/TiO₂/WO₃/CdS nanocatalyst and assess the effects of processing variables including RB19 concentration, catalyst concentration, pH, and irradiation time on the response. RB19 concentration and pH had the most and the second most significant role in the removal efficiency. While increasing the catalyst concentration and irradiation time positively enhanced the removal efficiency to more than 82%, increasing the pH and dye concentration showed the remarkable hindering effects on the removal efficiency by about 45% reduction. The reusability of the synthesized catalysts was studied under the optimum conditions as follows: [RB19] = 25 mg/L, [catalyst] = 1 g/L, pH of 4, and irradiation time = 2 h. The COD and TOC analyses were also conducted during photodegradation process. The COD and TOC removal efficiencies were achieved about 67% and 62%, respectively.

Post-fabrication structural changes and enhanced photodegradation activity of semiconductors@zeolite composites towards noxious contaminants

This review article provides the recent progress in semiconductor-based zeolite photoactive materials for the application of noxious contaminants removal. The rapidly expanding industrialization and globalization cause serious threats to the environment or water bodies. The semiconductor@zeolite photocatalysts were implemented for water quality management/sustainment. The exclusive properties of zeolite material have been elaborated with their role in the photocatalysis process. The photoactive material's properties like single-atom catalysts (SACs), distribution of metal in the zeolite crystal were elaborated along with their role in catalytic reactions. Differently prepared semiconductor@zeolite composites such as TiO₂@zeolite, binary and ternary composites, Fe/Ag/bismuth-modified/ZnO/ZnS/NiO/g-C₃N₄/core-shell/quantum dots modified zeolite composites, were systematically summarized. The research progress in morphologies, structural effect, degradation mechanism were recapitulated and tabulated form of % degradation with their optimal parameters such as catalyst dose, pollutant concentrations, pH, light source intensities were also provided. The significance of zeolite frameworks, the structural properties of semiconductor@zeolite photoactive materials to enhance the degradation efficiencies was explored. Analysis of the intermediate products of Norfloxacin, TCDD (2,3,7,8-tetrachlorodibenzo-p-dioxin), TCDF (2,3,7,8-tetrachlorodibenzofuran), diclofenac contaminants were systematically represented and structurally identified by GC-MS/HPLC-MS techniques.

Sustainable approaches for removal of cephalexin antibiotic from non-clinical environments: A critical review

In this article, the removal of cephalexin (CFX) antibiotic from non-clinical environment is reviewed. Adsorption and photocatalytic degradation techniques are widely used to remove CFX from waters and wastewaters, the combination of these methods is becoming more common for CFX removal. The treatment methods of CFX has not been reviewed before, the present article aim is to organize the scattered available information regarding sustainable approaches for CFX removal from non-clinical environment. These include adsorption by nanoparticles, bacterial biomass, biodegradation by bacterial enzymes and the photocatalysis using different catalysts and Photo-Fenton photocatalysis. The metal-organic frameworks (MOFs) appeared to have high potential for CFX degradation. It is evident from the recently papers reviewed that the effective methods could be used in place of commercial activated carbon. The widespread uses of photocatalytic degradation for CFX remediation are strongly recommended due to their engineering applicability, technical feasibility, and high effectiveness. The adsorption capacity of the CFX is ranging from 7 mg CFX g^-1 of activated carbon nanoparticles to 1667 mg CFX g^-1 of Nano-zero-valent iron from Nettle. In contrast, the photo-degradation was 45% using Photo-Fenton while has increased to 100% using heterogeneous photoelectro-Fenton (HPEF) with UVA light using chalcopyrite catalyst.

Palladium-Doped Tin Oxide Nanosensor for the Detection of the Air Pollutant Carbon Monoxide Gas

The exhaust gases from various sources cause air pollution, which is a leading contributor to the global disease burden. Hence, it has become vital to monitor and control the increasing pollutants coming out of the various sources into the environment. This paper has designed and developed a sensor material to determine the amount of carbon monoxide (CO), which is one of the major primary air pollutants produced by human activity. Nanoparticle-based sensors have several benefits in sensitivity and specificity over sensors made from traditional materials. In this study, tin oxide (SnO2), which has greater sensitivity to the target gas, is selected as the sensing material which selectively senses only CO. Tin oxide nanoparticles have been synthesized from stannous chloride dihydrate chemical compound by chemical precipitation method. Palladium, at the concentration of 0.1%, 0.2%, and 0.3% by weight, was added to tin oxide and the results were compared. Synthesized samples were characterized by X-ray diffraction (XRD) and field emission scanning electron microscope (FESEM) techniques. XRD revealed the tetragonal structure of the SnO2 nanoparticles and FESEM analysis showed the size of the nanoparticles to be about 7-20 nm. Further, the real-time sensor testing was performed and the results proved that the tin oxide sensor, doped with 0.2% palladium, senses the CO gas more efficiently with greater sensitivity.

Photocatalytic degradation of methylene blue with spent FCC catalyst loaded with ferric oxide and titanium dioxide

The spent fluid catalytic cracking (FCC) catalyst has been loaded with ferric oxide (Fe2O3) and titanium dioxide (TiO2). Fe-Ti/SF composite (loaded with 5 wt% TiO2 and 5 wt% Fe2O3), Fe/SF composite (loaded with10 wt% Fe2O3) and Ti/SF composite (loaded with 10 wt% TiO2) have been fabricated via a modified-impregnation method. The band gaps of the Fe-Ti/SF, Fe/SF and Ti/SF composites (evaluated by the energy versus [F(R∞)hv]n) are 2.23, 1.98 and 3.0 eV, respectively. Electrochemical impedance spectroscopy shows that the Fe-Ti/SF has lower electron transfer resistance, it has the small charge transfer resistance and fast charge transfer rate. The interparticle electrons transfer between the Fe2O3 and TiO2, which can improve the separation of the photo-electrons and holes. The holes transfer from valence band of TiO2 to the valence band of Fe2O3, which can provide more active sites around the adsorbed molecules. The methylene blue degradation efficiencies (with the Fe-Ti/SF, Fe/SF and Ti/SF composites) are ~ 94.2%, ~ 22.3% and ~ 54.0% in 120 min, respectively. This work reveals that the spent FCC catalyst as supporter can be loaded with Fe2O3 and TiO2. This composite is highly suitable for degradation of methylene blue, which can provide a potential method to dispose the spent FCC catalyst in industry.

Optimization and Analysis of Zeolite Augmented Electrocoagulation Process in the Reduction of High-Strength Ammonia in Saline Landfill Leachate

This work examined the behavior of a novel zeolite augmented on the electrocoagulation process (ZAEP) using an aluminum electrode in the removal of high-strength concentration ammonia (3471 mg/L) from landfill leachate which was saline (15.36 ppt) in nature. For this, a response surfaces methodology (RSM) through central composite designs (CCD) was used to optimize the capability of the treatment process. Design-Expert software (version 11.0.3) was used to evaluate the influences of significant variables such as zeolite dosage (100–120 g), current density (540–660 A/m2), electrolysis duration (55–65 min), and initial pH (8–10) as well as the percentage removal of ammonia. It is noted that the maximum reduction of ammonia was up to 71%, which estimated the optimum working conditions for the treatment process as follows: zeolite dosage of 105 g/L, the current density of 600 A/m2, electrolysis duration of 60 min, and pH 8.20. Furthermore, the regression model indicated a strong relationship between the predicted values and the actual experimental results with a high R2 of 0.9871. These results provide evidence of the ability of the ZAEP treatment as a viable alternative in removing high-strength landfill leachate of adequate salinity without the use of any supporting electrolyte.

Polyaniline-Grafted RuO2-TiO2 Heterostructure for the Catalysed Degradation of Methyl Orange in Darkness

Massive industrial and agricultural developments have led to adverse effects of environmental pollution resisting conventional treatment processes. The issue can be addressed via heterogeneous photocatalysis as witnessed recently. Herein, we have developed novel metal/semi-conductor/polymer nanocomposite for the catalyzed degradation and mineralization of model organic dye pollutants in darkness. RuO2-TiO2 mixed oxide nanoparticles (NPs) were modified with diphenyl amino (DPA) groups from the 4-diphenylamine diazonium salt precursor. The latter was reduced with ascorbic acid to provide radicals that modified the NPs and further served for in situ synthesis of polyaniline (PANI) that resulted in RuO2/TiO2-DPA-PANI nanocomposite catalyst. Excellent adhesion of PANI to RuO2/TiO2-DPA was noted but not in the case of the bare mixed oxide. This stresses the central role of diazonium compounds to tether PANI to the underlying mixed oxide. RuO2-TiO2/DPA/PANI nanocomposite revealed superior catalytic properties in the degradation of Methyl Orange (MO) compared to RuO2-TiO2/PANI and RuO2-TiO2. Interestingly, it is active even in the darkness due to high PANI mass loading. In addition, PANI constitutes a protective layer of RuO2-TiO2 NPs that permitted us to reuse the RuO2-TiO2/DPA/PANI nanocomposite nine times, whereas RuO2-TiO2/PANI and RuO2-TiO2 were reused seven and five times only, respectively. The electronic displacements at the interface of the heterojunction metal/semi-conductor under visible light and the synergistic effects between PANI and RuO2 result in the separation of electron-hole pairs and a reduction of its recombination rate as well as a significant catalytic activity of RuO2-TiO2/DPA/PANI under simulated sunlight and in the dark, respectively.