Robust visible light active CoNiO2-BiFeO3-NiS ternary nanocomposite for photo-fenton degradation of rhodamine B and methyl orange: Kinetics, degradation pathway and toxicity assessment

Nanocosmos of catalysis: a voyage through synthesis, properties, and enhanced photocatalytic degradation in nickel sulfide nanocomposites

Nanomaterials play a decisive role in environmental applications such as water purification, pollutant monitoring, and advanced oxidation-based remediation processes, particularly in semiconductor and metal sulfide-based photocatalysis. Metal sulfides are ideal for photocatalysis because of their unique optical, structural, and electronic characteristics. These properties enable the effective use of solar energy to drive various catalytic reactions with potential uses in environmental remediation with sustainable energy production. Among them, nickel sulfides (NiS) stand out for their narrow band gaps, high stability, and cost-effectiveness. This review thoroughly analyzes recent advancements in employing nickel-sulfide-based nanostructures for water decontamination. It begins by addressing environmental material needs and emphasizing the properties of nickel sulfide. To improve photocatalytic performance, controlled processes that affect the active structure, shape, composition, and size of nickel sulfide photocatalysts are examined, along with their synthesis methods. The heart of the review article is a detailed analysis of the modification of NiS through metal and non-metal doping, heterojunction, and nanocomposite formation for enhanced photocatalytic performance. The discussion also includes metal-modified nanostructures, metal oxides, and carbon-hybridized nanocomposites. This study underscores notable advancements in the degradation efficiency of NiS photocatalysts, rivaling their costly noble-metal counterparts. The analysis concludes with potential future directions for nickel sulfide-based photocatalysts in sustainable environmental remediation.

Novel magnetic nanocomposites BiFeO3/Cu(BDC) for efficient dye removal

In this study, bismuth ferrite nanoparticles and metal-organic framework, Cu(BDC), were prepared by microwave-assisted combustion in solid state and ultrasound-assisted method, respectively. To enhance the properties of bismuth ferrite nanoparticles and Cu(BDC), we form them as their composite through microwave and ultrasonic probe strategies. Various analyses, including FT-IR, XRD, SEM, DRS, VSM, and so on, were applied to verify the synthesis accuracy. Then, the catalytic performances of the nanoparticles and the as-prepared nanocomposites were evaluated through photocatalytic degradation of methyl orange. Furthermore, the adsorption capacity of the as-synthesized materials was assessed toward the Congo red removal from wastewater. All the results prove that the proposed nanocomposite can be an acceptable candidate for eliminating contaminants from wastewater. The electrochemical properties of bismuth ferrite, BiFeO3/Cu(BDC) nanocomposite 1, and BiFeO3/Cu(BDC) nanocomposite 2 have been studied by cyclic voltammetry.

Boosted Photocatalytic Performance for Antibiotics Removal with Ag/PW12/TiO2 Composite: Degradation Pathways and Toxicity Assessment

Photocatalyst is the core of photocatalysis and directly determines photocatalytic performance. However, low quantum efficiency and low utilization of solar energy are important technical problems in the application of photocatalysis. In this work, a series of polyoxometalates (POMs) [H3PW12O40] (PW12)-doped titanium dioxide (TiO2) nanofibers modified with various amount of silver (Ag) nanoparticles (NPs) were prepared by utilizing electrospinning/photoreduction strategy, and were labelled as x wt% Ag/PW12/TiO2 (abbr. x% Ag/PT, x = 5, 10, and 15, respectively). The as-prepared materials were characterized with a series of techniques and exhibited remarkable catalytic activities for visible-light degradation tetracycline (TC), enrofloxacin (ENR), and methyl orange (MO). Particularly, the 10% Ag/PT catalyst with a specific surface area of 155.09 m2/g and an average aperture of 4.61 nm possessed the optimal photodegradation performance, with efficiencies reaching 78.19% for TC, 93.65% for ENR, and 99.29% for MO, which were significantly higher than those of PW12-free Ag/TiO2 and PT nanofibers. Additionally, various parameters (the pH of the solution, catalyst usage, and TC concentration) influencing the degradation process were investigated in detail. The optimal conditions are as follows: catalyst usage: 20 mg; TC: 20 mL of 20 ppm; pH = 7. Furthermore, the photodegradation intermediates and pathways were demonstrated by HPLC-MS measurement. We also investigated the toxicity of products generated during TC removal by employing quantitative structure-activity relationship (QSAR) prediction through a toxicity estimation software tool (T.E.S.T. Version 5.1.2.). The mechanism study showed that the doping of PW12 and the modification of Ag NPs on TiO2 broadened the visible-light absorption, accelerating the effective separation of photogenerated carriers, therefore resulting in an enhanced photocatalytic performance. The research provided some new thoughts for exploiting efficient and durable photocatalysts for environmental remediation.

Algae-derived metal-free boron-doped biochar acts as a catalyst for the activation of peroxymonosulfate toward the degradation of diclofenac

In this study, plain seaweed biochar (SW) and boron-doped seaweed biochar (BSW) were prepared through a simple pyrolysis process using Undaria pinnatifida (algae biomass) and boric acid. The BSW catalyst was utilized to degrade organic pollutants in aqueous environments by activating peroxymonosulfate (PMS). Surface characterization of the BSW demonstrated successful doping of boron into the biochar materials. BSW₆₀₀ exhibited greater catalytic activity than SW₆₀₀, as evidenced by the former's maximum adsorption capacity of diclofenac (DCF) onto BSW₆₀₀ (q_max = 30.01 mg g^-1) and the activation of PMS. Complete degradation of DCF was achieved in 30 min using 100 mg L^-1 BSW₆₀₀, 0.5 mM PMS, and 6.5 initial solution pH as critical parameters. The pseudo-first-order kinetic model accurately described the DCF degradation kinetics. The scavenger experiment displayed that radical and non-radical reactive oxygen species (ROS) formed in the BSW₆₀₀/PMS system. Furthermore, the generation of ROS in the BSW₆₀₀/PMS system was confirmed by electron spin resonance spectroscopy (ESR). The percentage contribution of ROS was assessed to be 10, 65, and 25% for HO^•, SO₄^•-, and ¹O₂, respectively. Additionally, the electron transfer pathway was also confirmed by electrochemical analysis. Moreover, the influence of water matrics on the BSW₆₀₀/PMS system was demonstrated. The co-existence of anions and humic acid (HA) did not affect the catalytic activity of the BSW₆₀₀/PMS system. The recyclability of BSW₆₀₀ was assessed by DCF removal (86.3%) after three cycles. Ecological structure-activity relationships software was used to assess by-product toxicity. This study demonstrates the efficacy of non-metallic heteroatom-doped biochar materials as eco-friendly catalysts in groundwater applications.

Engineered ball-milled colloidal activated carbon material for advanced oxidation process of ibuprofen: Influencing factors and insights into the mechanism

This study explores a simple and efficient, physically modified ball-milled activated carbon (AC_BM) preparation from granular activated carbon (GAC), which can be demonstrated for groundwater application. The colloidal stability of the AC_BM plays a vital role in the activation of peroxymonosulfate (PMS) and the degradation of pollutants. Adsorption kinetics and isotherm studies explain that the AC_BM has more active sites and maximum adsorption capacity (q_max = 509 mg g^-1) on the surface of the materials than GAC. The 92% of ibuprofen degradation was achieved at 240 min along with 0.1 g L^-1 of AC_BM, 5 mM of PMS, and 6.3 of initial solution pH. A chemical scavenger and electron spin resonance spectra also confirmed the formation of reactive oxygen species such as radicals (O₂^•-, HO^•, SO₄^•-) and non-radical (¹O₂) in the AC_BM/PMS system. Three major degradation pathways, hydroxylation, demethylation, and decarboxylation involved in ibuprofen degradation. Nearly 13 degradation by-products were detected during the AC_BM/PMS oxidation of ibuprofen. The toxicity analysis of oxidation by-products of ibuprofen was also discussed by computational simulation employing the ecological structure-activity relationships software. The AC_BM/PMS system was successfully applied to the natural groundwater system for ibuprofen degradation. Hence, the AC_BM/PMS system is an excellent catalyst for real groundwater applications.

Abatement of paraquat contaminated water using solar assisted heterogeneous photo-Fenton like treatment with iron-containing industrial wastes as catalysts

Owing to the tremendous increase of chemicals for agricultural practices, the quality of water has degraded significantly and requires inevitable attention. With this in mind, present work aims at treating Paraquat (PQ) contaminated water using Fe containing industrial waste as a catalyst via photo-Fenton treatment. Utilizing the industrially generated Fe rich waste by-products i.e., Fly ash (FA), Foundry sand (FS), Red mud (RM), and Blast sand (BS) as catalysts marks the novelty of the work since this idea of using waste for treating waste serves the dual purpose of environment remediation:first by treating wastewater and second by resolving the issue of solid waste disposal. In the present study, 25 mg/L PQ was subjected to both UV and solar radiations in the presence of FeSO₄, FA, FS, RM, and BS as catalysts. The presence of Fe in the catalysts was verified using analytical techniques namely FTIR, FESEM-EDX, and their XRD was also analyzed. The system was further optimized for various parameters and results indicated maximum PQ degradation under UV radiations was attained in the order FeSO₄ (73%) > BS (65%) > FS (46%) > RM (37%) > FA (14%) within 60 min which significantly increased with introduction of solar radiations to 83% for Fe salt and 76% for BS justifying the potential of using waste for treating waste. Further, to enhance the real-life utilization of industrial waste, Fe₂O₃/BS heterojunction (Fe-BS) was synthesized which along with leading to 88% degradation of PQ, also showed 82% COD removal indicating that the catalyst not only degrades the pollutant but also converts it into a lower toxic form. Further, the intermediates formed during the process were analyzed using LCMS.

Green Synthesis of NiO-SnO2 Nanocomposite and Effect of Calcination Temperature on Its Physicochemical Properties: Impact on the Photocatalytic Degradation of Methyl Orange

Background: Nickel stannate nanocomposites could be useful for removing organic and toxic water pollutants, such as methyl orange (MO). Aim: The synthesis of a nickel oxide-tin oxide nanocomposite (NiO-SnO₂ NC) via a facile and economically viable approach using a leaf extract from Ficus elastica for the photocatalytic degradation of MO. Methods: The phase composition, crystallinity, and purity were examined by X-ray diffraction (XRD). The particles' morphology was studied using scanning electron microscopy (SEM). The elemental analysis and colored mapping were carried out via energy dispersive X-ray (EDX). The functional groups were identified by Fourier transform infrared spectroscopy (FTIR). UV-visible diffuse reflectance spectroscopy (UV-vis DRS) was used to study the optical properties such as the absorption edges and energy band gap, an important feature of semiconductors to determine photocatalytic applications. The photocatalytic activity of the NiO-SnO₂ NC was evaluated by monitoring the degradation of MO in aqueous solution under irradiation with full light spectrum. The effects of calcination temperature, pH, initial MO concentration, and catalyst dose were all assessed to understand and optimize the physicochemical and photocatalytic properties of NiO-SnO₂ NC. Results: NiO-SnO₂ NC was successfully synthesized via a biological route using F. elastica leaf extract. XRD showed rhombohedral NiO and tetragonal SnO₂ nanostructures and the amorphous nature of NiO-SnO₂ NC. Its degree of crystallinity, crystallite size, and stability increased with increased calcination temperature. SEM depicted significant morphological changes with elevating calcination temperatures, which are attributed to the phase conversion from amorphous to crystalline. The elemental analysis and colored mapping show the formation of highly pure NiO-SnO₂ NC. FTIR revealed a decrease in OH, and the ratio of oxygen vacancies at the surface of the NC can be explained by a loss of its hydrophilicity at increased temperatures. All the NC samples displayed significant absorption in the visible region, and a blue shift is seen and the energy band gap decreases when increasing the calcination temperatures due to the dehydration and formation of compacted large particles. NiO-SnO₂ NC degrades MO, and the photocatalytic performance decreased with increasing calcination temperature due to an increase in the crystallite size of the NC. The optimal conditions for the efficient NC-mediated photocatalysis of MO are 100 °C, 20 mg catalyst, 50 ppm MO, and pH 6. Conclusions: The auspicious performance of the NiO-SnO₂ NCs may open a new avenue for the development of semiconducting p-n heterojunction catalysts as promising structures for removing undesirable organic pollutants from the environment.

A Novel Shift in the Absorbance Maxima of Methyl Orange with Calcination Temperature of Green Tin Dioxide Nanoparticle-Induced Photocatalytic Activity

Background: The photocatalytic degradation of toxic organic compounds has received great attention for the past several years. Dyes, such as methyl orange (MO), are one of the major pollutants which create environmental hazards in the hydrosphere, living organisms and human beings. During photocatalytic degradation, NPs are activated in the presence of UV–Vis radiation which in turn creates a redox environment in the system and behaves as a sensitizer for light-induced redox mechanisms. Tin oxide (SnO2) is one of the prominent, but less investigated, nanomaterials compared to titanium oxide (TiO2) and Zinc oxide (ZnO) nanoparticles (NPs). Methods: Herein, Buxus wallichiana (B. wallichiana) leaf extract was utilized as a reducing and capping agent for the biosynthesis of SnO2 NPs. The effects of the calcination temperature on their photocatalytic, structure and surface properties were then examined. The degree of crystallinity and the crystallite size were determined through X-ray diffraction (XRD) analysis. The pore size and surface area were calculated by Burnett–Emmitt–Teller (BET) and Barrett–Joyner–Halenda (BJH) methods based on nitrogen desorption data. Morphological changes were assessed by scanning electron microscopy (SEM). The optical behavior was analyzed through UV–Vis diffuse reflectance spectroscopy (DRS) data and the band gap subsequently calculated. The photocatalytic efficiency of SnO2 NPs was evaluated by double beam UV–Vis spectrophotometry under the influence of initial MO concentration, catalyst dose and pH of MO solution. The surface functional moieties were identified using Fourier transform infrared (FTIR) spectroscopy. All the calcined SnO2 NPs were used as photocatalysts for the mineralization of MO in aqueous media. Results: The degree of crystallinity and the crystallite size increased with the calcination temperature. The transmittance edge obtained for all the calcined SnO2 NPs shows a maximum absorbance in the visible range (λ-max = 464 nm). Moving toward higher wavelengths, a sudden intense red shift (from 464 nm to 500 nm), attributed to the incorporation of a hydroxyl radical at the ortho-position in the benzene ring associated with the dimethylamine group of MO, was observed in the absorbance of the samples calcined up to 300 °C. The percentage degradation of MO was found to decrease with increasing calcination temperatures. The optimal photocatalytic activity toward MO (15 ppm) in a solution of pH = 6 was obtained with 15 mg SnO2 NPs calcined at 100 °C. Conclusions: UV–Vis absorption spectroscopy demonstrates that the absorption spectra of MO are strongly modified by the calcination temperature. This work opens new avenues for the use of SnO2 NPs as photocatalysts against the degradation of industrial effluents enriched with different dyes.