Synthesis of Fe-doped Bi2O3 nanocatalyst and its sonophotocatalytic activity on synthetic dye and real textile wastewater

Sono-assisted photocatalytic degradation of ciprofloxacin in aquatic media using g-C3N4/MOF-based nanocomposite under visible light irradiation

This research study is centered on the sono-assisted photocatalytic degradation of a well-known antibiotic (ciprofloxacin; CIP) in aquatic media using a g-C3N4/NH2-UiO-66 (Zr) catalyst under visible light irradiation. Initially, the catalyst was prepared by a simple method, and its physiochemical features were thoroughly analyzed by XRD, FT-IR, FE-SEM, EDX, EDS-Dot-Mapping, and UV-Vis analytical techniques. After that, the impact of several influential factors affecting the performance of the applied sono-assisted photocatalytic process such as the initial concentration of CIP, solution pH, catalyst dosage, light intensity, and ultrasound power was fully assessed, and the optimal conditions were established. After 75 min of the sono-assisted photocatalytic treatment, the complete degradation of CIP (10 mg/L) was accomplished under the condition as follows: g-C3N4/NH2-UiO-66 (Zr), 0.6 g/L; pH, 5.0, and ultrasound power, light intensity 75 mw/cm2, 200 W/m2. Meanwhile, the photocatalytic degradation of CIP followed the pseudo-first-order kinetic model. In addition, the scavenger experiments demonstrated that OH˚ and O2°- radicals played a key role in the sono-assisted photocatalytic degradation process. It is also acknowledged that the applied catalyst was reused for five consecutive runs with a minor loss observed in its degradation efficiency. In a further experiment, a significant synergistic effect with regard to the degradation of CIP was observed once all three major parameters (visible light, ultrasound waves, and catalyst) were used in combination compared to each used alone. To sum up, it is thought that the integration of g-C3N4/MOF-based catalyst, ultrasound waves, and visible light irradiation could be potentially applied as a promising strategy for the degradation of various pharmaceuticals on account of high degradation performance, simple operation, excellent reusability, and eco-friendly approach.

Enhanced degradation of chloramphenicol via heterogeneous activation of peroxymonosulfate by Fe3O4 and gallic acid

In this study, we demonstrated the effective degradation of wide-spectrum antibiotic chloramphenicol (CAP) by Fe3O4/peroxymonosulfate (PMS) system modified by gallic acid (GA). GA/Fe3O4/PMS showed a substantially higher degradation rate (77.6%) than Fe3O4/PMS (8.3%). The active components were detected by electron spin-resonance spectroscopy (ESR) and the quenching experiments. The results showed that the hydroxyl radical (HO•) was the main reason for the degradation of CAP. In the GA/Fe3O4/PMS system, the trace amount of dissolved iron ion were not the main species that activated PMS. Surface characterization and theoretical simulations showed that Fe atoms on Fe3O4 were responsible for PMS activation rather than a homogenous reaction. Five probable CAP degradation pathways were identified by density functional theory (DFT) calculations and liquid-phase mass spectrometry. Finally, the reusability of Fe3O4 was measured, and the GA/Fe3O4/PMS system maintained high efficiency after 5 times applications. The total organic carbon (TOC) removal rate reached 46.5% after reacting for 12 h. The gallic acid effectively promotes the circulation of Fe(II)/Fe(III) on solid surfaces and enhanced the degradation capacity of the original system. The research proposed a new way of directly employing plant polyphenols to boost the degradation ability of contaminants in heterogeneous systems.

Generation and engineering applications of sulfate radicals in environmental remediation

Sulfate radical (SO4•-)-based advanced oxidation processes (AOPs) have become promising alternatives in environmental remediation due to the higher redox potential (2.6-3.1 V) and longer half-life period (30-40 μs) of sulfate radicals compared with many other radicals such as hydroxyl radicals (•OH). The generation and mechanisms of SO4•- and the applications of SO4•--AOPs have been examined extensively, while those using sulfite as activation precursor and their comparisons among various activation precursors have rarely reviewed comprehensively. In this article, the latest progresses in SO4•--AOPs were comprehensively reviewed and commented on. First of all, the generation of SO4•- was summarized via the two activation methods using various oxidant precursors, and the generation mechanisms were also presented, which provides a reference for guiding researchers to better select two precursors. Secondly, the reaction mechanisms of SO4•- were reviewed for organic pollutant degradation, and the reactivity was systematically compared between SO4•- and •OH. Thirdly, methods for SO4•- detection were reviewed which include quantitative and qualitative ones, over which current controversies were discussed. Fourthly, the applications of SO4•--AOPs in various environmental remediation were summarized, and the advantages, challenges, and prospects were also commented. At last, future research needs for SO4•--AOPs were also proposed consequently. This review could lead to better understanding and applications of SO4•--AOPs in environmental remediations.

Co+2, Ni+2 and Cu+2 incorporated Bi2O3 nano photocatalysts: Synthesis, DFT analysis of band gap modification, adsorption and photodegradation analysis of rhodamine B and Triclopyr

This study deals with the fabrication of metal ion (M = Co+2, Ni+2, and Cu+2) doped- Bi2O3 photocatalysts by solution combustion method. All the synthesized materials were characterized and analysed with the help of XRD, FESEM, EDX, HRTEM, UVDRS, Zeta potential, PL, and LCMS techniques for the structural, morphological, surface charge, optical and degradation pathways characteristics. Synthesized compounds were used for the decontamination (adsorption and degradation) of two organic pollutants namely Rhodamine B and Triclopyr. Adsorption aspects of the pollutants were studied in terms of different isotherm, kinetic and thermodynamic models. Adsorption phenomenon was best fitted with the Freundlich (R2 = 0.992) and Langmuir isotherm (R2 = 0.999) models along with pseudo second order model of kinetics for RhB and TC, respectively. Moreover, the thermodynamic parameters indicated exothermic and endothermic adsorption (ΔH ° (-7.19 kJ/mol) for RhB) and (ΔH ° (52.335 kJ/mol) for TC), respectively. Evaluated negative values of ΔG ° indicated spontaneous adsorption with most favourable at 298 K and 318 K for both the pollutants (RhB and TC) respectively. Modification with metal ions significantly improved the removal efficiency of pure Bi2O3 photocatalyst and followed the trend Co+2/Bi2O3 > Ni+2/Bi2O3 > Cu+2/Bi2O3 > Bi2O3. DFT calculations demonstrate that amongst the doped materials, only Co+2/Bi2O3 is characterized by an indirect band gap; which exhibited efficacious photocatalytic activity. Besides, the highest degradation efficiency was obtained in the case of Co+2/Bi2O3 (2 mol %); being 99.80% for RhB in 30 min and 98.50% for TC in 60 min, respectively. The doped nanostructures lead to higher absorption of visible light and more separation of light-induced charged carriers. Effect of pH of the reaction medium and role of reactive oxygen species was also examined. Finally, a probable mechanism of charge transfer and degradation of the pollutants was also presented.

Sonophotocatalysis with Photoactive Nanomaterials for Wastewater Treatment and Bacteria Disinfection

Sonophotocatalysis is described as a combination of two individual processes of photocatalysis and sonocatalysis. It has proven to be highly promising in degrading dissolved contaminants in wastewaters as well as bacteria disinfection applications. It eliminates some of the main disadvantages observed in each individual technique such as high costs, sluggish activity, and prolonged reaction times. The review has accomplished a critical analysis of sonophotocatalytic reaction mechanisms and the effect of the nanostructured catalyst and process modification techniques on the sonophotocatalytic performance. The synergistic effect between the mentioned processes, reactor design, and the electrical energy consumption has been discussed due to their importance when implementing this novel technology in practical applications, such as real industrial or municipal wastewater treatment plants. The utilization of sonophotocatalysis in disinfection and inactivation of bacteria has also been reviewed. In addition, we further suggest improvements to promote this technology from the lab-scale to large-scale applications. We hope this up-to-date review will advance future research in this field and push this technology toward widespread adoption and commercialization.

Comparative Study of Sonophotocatalytic, Photocatalytic, and Catalytic Activities of Magnesium and Chitosan-Doped Tin Oxide Quantum Dots

The present study demonstrates the hydrothermal synthesis of SnO₂ quantum dots (QDs) doped with different concentrations (2, 4 wt %) of magnesium (Mg) and a fixed amount of chitosan (CS). The obtained samples were investigated through a number of characterizations for optical analysis, elemental composition, crystal structure, functional group presence, interlayer spacing, and surface morphology. The XRD spectrum revealed the tetragonal structure of SnO₂ with no significant variations occurring upon the addition of CS and Mg. The crystallite size of QDs was reduced by incorporation of dopants. The optical absorption spectra revealed a red shift, assigned to the reduction of the band gap energy upon doping. TEM analysis proved that the few nanorod-like structures of CS overlapped with SnO₂ QDs, and agglomeration was observed upon Mg doping. The incorporation of dopants little enhanced the d-spacing of SnO₂ QDs. Moreover, the synthesized nanocatalyst was utilized to calculate the degradation percentage of methylene blue (MB) dye. Afterward, a comparative analysis of catalytic activity, photocatalytic activity, and sonophotocatalytic activity was carried out. Notably, 4% Mg/CS-doped QDs showed maximum sonophotocatalytic degradation of MB in basic medium compared to other activities. Lastly, the prepared nanocatalyst was found to be efficient for dye degradation in any environment and inexpensive.

Recent Progress and Prospects in Catalytic Water Treatment

Presently, conventional technologies in water treatment are not efficient enough to completely mineralize refractory water contaminants. In this context, the implementation of catalytic processes could be an alternative. Despite the advantages provided in terms of kinetics of transformation, selectivity, and energy saving, numerous attempts have not yet led to implementation at an industrial scale. This review examines investigations at different scales for which controversies and limitations must be solved to bridge the gap between fundamentals and practical developments. Particular attention has been paid to the development of solar-driven catalytic technologies and some other emerging processes, such as microwave assisted catalysis, plasma-catalytic processes, or biocatalytic remediation, taking into account their specific advantages and the drawbacks. Challenges for which a better understanding related to the complexity of the systems and the coexistence of various solid-liquid-gas interfaces have been identified.

Degradation of amoxicillin with sono, photo, and sonophotocatalytic oxidation under low-frequency ultrasound and visible light

The presence of pharmaceutically active compounds in aquatic bodies is a global concern, and suitable treatment technologies are required. In this study, the efficacy of photocatalytic, sonocatalytic, and sonophotocatalytic oxidation processes for the degradation of amoxicillin (AMX) was investigated using visible light with N doped TiO₂ (N-TiO₂) nanoparticles as the catalyst and low-frequency ultrasound in a novel multifrequency reactor. The influence of different operational parameters on the extent of AMX degradation was studied. Sonophotocatalytic oxidation was found more efficient for AMX degradation when compared to photocatalysis or sonocatalysis alone, and may be due to the reduced bandgap of the catalyst, enhanced cavitation effect due to the presence of the solid catalyst, and improved mass transfer of pollutants. AMX degradation during sono, photo, and sonophotocatalytic oxidation processes was in good agreement with pseudo-first-order kinetics. Empirical kinetic models were also developed using multiple linear regression for predicting the degradation efficiency accounting for the operational parameters. Scavenger experiments suggested that ^•OH radicals largely contributed to AMX degradation, and a plausible mechanism for degradation was proposed. Further, possible degradation pathways for all three treatment processes are also proposed after identifying the degradation products.

A critical analysis of sono-hybrid advanced oxidation process of ferrioxalate system for degradation of recalcitrant pollutants

The emerging contaminants in wastewater discharged from numerous chemical process industries, pharmaceutical industries, textile, and wineries have attracted the attention of the scientific community due to their toxicity and persistence in the environment. The conventional techniques are incompetent to treat many of such recalcitrant toxic pollutants. To achieve high mineralization, advanced oxidation processes (AOPs) are found to be more efficient for the degradation of these organic pollutants without producing secondary pollutants with no/less amount of sludge. The primary oxidation agents for AOPs are in-situ generated free radicals, which are highly reactive and effective oxidants for degrading any type of organic molecules present in the wastewater. In the past decades, the combination of AOPs or simultaneous application of more than one AOP has been investigated extensively for wastewater treatment and these hybrid-AOPs have been reported to be beneficial for high-level mineralization of organic pollutants. This paper presented the characteristics, properties and influence of parameters in sono-photo-ferrioxalate system. The primary operating parameters in sono-photo-ferrioxalate system that affect the kinetics are defined as the solution pH, temperature, molar ratio of Fe³⁺/C₂O₄^2-, H₂O₂ concentration, source of light, ultrasound intensity, dissolved gases, and size of cavitation bubble. In this process, several oxidizing radicals are generated such as HO^•, HO₂^•, C₂O₄^•-, CO₂^•- and O₂^•- which are also responsible for degradation. In this review, we have mainly addressed the degradation of recalcitrant pollutants using the sono-photo-ferrioxalate system and a critical analysis of process parameters that influence mineralization efficiency.

Catalytic activity comparison of natural ferrous minerals in photo-Fenton oxidation for tertiary treatment of dyeing wastewater

Natural ferrous minerals are readily available and recyclable catalysts in photo-Fenton-like oxidation for wastewater treatment. In this work, typical ferrous oxide and sulfide minerals including magnetite, chalcopyrite, and pyrrhotite were exploited as catalysts in heterogeneous photo-Fenton oxidation for purification of biological effluent of dyeing wastewater. In a wide initial pH range (3.0~7.5), ferrous mineral-based heterogeneous photo-Fenton-like reactions were proven to be effective on the oxidation of recalcitrant pollutants. COD removals achieved 60.57%, 58.83%, and 57.41% using pyrrhotite, chalcopyrite, and magnetite, respectively, as catalyst under ultraviolet irradiation of 220~275 nm at H₂O₂ concentration of 9.8 mM. The corresponding COD removals were 51.75% and 34.09% with or without ferrous sulfate additions in UV/H₂O₂ systems. Minerals exhibited excellent stability and reusability with photo-catalytic activity reduction of less than 10% in the reuse of 5 cycles. Dissolved iron concentrations were determined to be 1.86 mg L^-1, 4.62 mg L^-1, and 7.53 mg L^-1 for magnetite, chalcopyrite, and pyrrhotite, respectively, at pH 3 and decreased to zero in neutral pH environment, which were much lower than those required for homogenous Fenton reaction. It was deduced that oxidation of recalcitrant pollutants was mainly catalyzed by Fe(II) on the mineral surface. The more reactive oxygen species such as hydroxyl radicals were resulted from the reaction of surface Fe (II) with H₂O₂, H₂O₂ photolysis, and charge separation of minerals under UV irradiation.

Hybrid Advanced Oxidation Processes Involving Ultrasound: An Overview

Sonochemical oxidation of organic pollutants in an aqueous environment is considered to be a green process. This mode of degradation of organic pollutants in an aqueous environment is considered to render reputable outcomes in terms of minimal chemical utilization and no need of extreme physical conditions. Indiscriminate discharge of toxic organic pollutants in an aqueous environment by anthropogenic activities has posed major health implications for both human and aquatic lives. Hence, numerous research endeavours are in progress to improve the efficiency of degradation and mineralization of organic contaminants. Being an extensively used advanced oxidation process, ultrasonic irradiation can be utilized for complete mineralization of persistent organic pollutants by coupling/integrating it with homogeneous and heterogeneous photocatalytic processes. In this regard, scientists have reported on sonophotocatalysis as an effective strategy towards the degradation of many toxic environmental pollutants. The combined effect of sonolysis and photocatalysis has been proved to enhance the production of high reactive-free radicals in aqueous medium which aid in the complete mineralization of organic pollutants. In this manuscript, we provide an overview on the ultrasound-based hybrid technologies for the degradation of organic pollutants in an aqueous environment.

Mechanistic investigation in degradation mechanism of 5-Fluorouracil using graphitic carbon nitride

The present study reports the synthesis of metal-free polymeric catalyst, graphitic carbon nitride (g-C₃N₄), through sonochemical method followed by thermal treatment. The synthesized g-C₃N₄ was characterized using XRD, DRS, FESEM, TGA, EDX, etc. and the characterization results revealed that it possesses medium band-gap energy, high thermal and chemical stability. The photo-activity of the catalyst was also evaluated using degradation of 5-Fluorouracil under different experimental conditions. The results revealed that the addition of H₂O₂ during sonolysis process did not show any significant synergy. This is attributed to the low vapor pressure of H₂O₂ that does not allow it to diffuse into the cavitation bubble to produce OH radicals through sonolysis process. Using sono-hybrid process, more than 90% degradation was seen within 5 min of treatment with a rate constant of 3.95 × 10^-2 s^-1. In alkaline medium, 5-Fluorouracil degradation occurred through defluorination and subsequently substitution of -OH group to the aromatic ring leading to formation of intermediates such as 2-fluoro-3-oxopropanoic acid and urea. While sono-hybrid advanced oxidation processes (AOPs) helped towards complete mineralization through formation of smaller molecular compounds such as maleic acids, lactic acids, propanol, etc. On the other hand, the maximum synergy effect of ∼2.4 was seen for sonocatalysis process followed by hybrid-AOPs of (US + g-C₃N₄ + H₂O₂ + UVC) with a synergy factor of ∼2.2. Also, the synthesized catalyst exhibited the same catalytic activity even after 5 runs of sono-photocatalysis process for degradation of 5-Fluorouracil.

Fabrication of graphene-oxide/β-Bi2O3/TiO2/Bi2Ti2O7 heterojuncted nanocomposite and its sonocatalytic degradation for selected pharmaceuticals

A graphene-oxide (GO)/β-Bi₂O₃/TiO₂/Bi₂Ti₂O₇ heterojuncted nanocomposite, designated as GBT, was synthesized via a two-step hydrothermal process. The sonocatalytic activity of the GBT was evaluated at several frequencies (28, 580, and 970 kHz) and compared with Bi-doped GO (GB) and Ti-doped GO (GT). Transmission electron microscopy images showed heterojuncted crystal structures of Bi and Ti on GO, and X-ray diffraction patterns verified that the crystal structures consisted of β-Bi₂O₃, TiO₂, and Bi₂Ti₂O₇ nanocomposites. Energy-dispersive X-ray spectroscopy revealed a higher proportion of metal on GBT surfaces compared with GB and GT surfaces. The energy band gaps of GT, GB, and GBT were 3.0, 2.8, and 2.5 eV, respectively. Two pharmaceuticals (PhACs; carbamazepine [CBZ] and acetaminophen [ACE]) were selected and treated under sonolytic conditions at frequencies of 28, 580, and 970 kHz at a power level of 180 W L^-1. The selected pharmaceuticals, present at initial concentrations of 20 μM, were reduced by over 99% by ultrasonic irradiation in the presence of GBT. The 580 kHz treatment achieved the most rapid organic removal among the frequencies tested. The removal kinetic of CBZ was higher than that of ACE owing to its relatively high hydrophobicity. High sonocatalytic activity of GBT was observed through measurement of H₂O₂ in solution. Because of its low band gaps and high surface activity, GBT exhibited higher sonolytic activity in removing selected PhACs than GT or GB.

Influence of aromatic additives on Bismarck Brown Y dye color removal treatment by Fenton processes

The influence of diverse aromatic additives on Fenton processes (Fe²⁺/H₂O₂, Fe³⁺/H₂O₂) has been evaluated by using the Bismarck Brown Y (BBY) di azo dye as target pollutant. Results indicate that all tested Fe³⁺-reducing additives (gallic, 3,4-dihydroxyphenylacetic, 2,3-dihydroxybenzoic, and 2,5-dihydroxybenzoic acids, catechol, and hydroquinone) exhibited pro-oxidant properties during BBY dye color removal, mainly during Fe³⁺/H₂O₂ treatments. For example, in the presence of hydroquinone BBY color removal was increased from 22 to 83% for 60 min through the Fe³⁺/H₂O₂ process. The effect of non-reducing additives was less pronounced, among which salicylic and 2,4-dihydroxybenzoic acids were more efficient at removing dye color than benzoic acid and methylene blue. It was suggested that OH radicals may have converted non-reducing additives into Fe³⁺-reducing intermediates, which had a positive effect on the treatments. On the other hand, antioxidant properties were observed during BBY color removal in the presence of higher concentrations of gallic and salicylic acids. These items of data indicate that a minimum amount of aromatic additive was enough to increase BBY dye color removal by Fenton processes.