Sunlight-Driven Combustion Synthesis of Defective Metal Oxide Nanostructures with Enhanced Photocatalytic Activity

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.

Progressive yield of nickel cobaltite nanocubes for visible light utilization and degrading activities of methyl orange dye pollutant

In this study, pure cobalt oxide (Co₃O₄) as well as nickel cobaltite (NiCo₂O₄) were investigated with their capacity of degradation efficiency for textile dyes like methyl orange (MO) employing visible light irradiation. Two variable concentrations of nickel cobaltite (NiCo₂O₄) with 75:25 and 50:50 wt ratios along with the pure metal oxides were synthesized by thermal decomposition method and analyzed by various sophisticated instruments. Initially, the structural characteristics described the fine crystalline nature of NiCo₂O₄ and also exhibits reduced size than the pure component material (Co₃O₄). Besides, NiCo₂O₄ catalysts represented nano cubic shaped particles, and also their coordinating functional groups were evaluated. Further, the absorption wavelength confirms the two band positions of NiCo₂O₄ which leads to promote visible light absorption, and degrading efficiency of about 47.5% for NiCo₂O₄ (75:25) sample compared with NiCo₂O₄ (50:50) which produced only 26.3% degradation. This higher efficiency of the former was due to high crystallinity and interfacial charge transfer of combined Ni²⁺, Ni³⁺, Co²⁺ and Co³⁺ redox couples. This consecutively produces effective OH radicals that brought the degradation effectively under visible light. The recycling capacity up to 5 repeated cycles has been studied with the NiCo₂O₄ (75:25) and therefore the catalyst can further be used in other dye degradation.

Synthesis and characterization of SSM@NiO/TiO2 p-n junction catalyst for bisphenol a degradation

Photocatalyst immobilization on support materials is essential for large-scale applications. Here, we describe growth of a p-n junction catalyst (NiO/TiO₂) on a stainless-steel mesh (SSM) support using a facile hydrothermal method. The morphological superiority of the composite over previously reported NiO/TiO₂ catalysts was probed using scanning and transmission electron microscopy. Flower petal-like NiO grew uniformly on SSM, which was evenly covered by TiO₂ nanoparticles. Theoretical and experimental X-ray diffraction patterns were compared to analyze the development of the composite during various stages of synthesis. The photocatalytic activity of a powdered catalyst and SSM@catalyst was compared by measuring bisphenol A (BPA) degradation. SSM@NiO/TiO₂ achieved the highest rate of BPA degradation, removing 96% of the BPA in 120 min. Scavenging experiments were used to investigate the charge separation and degradation mechanism. SSM@NiO/TiO₂ showed excellent reusability potential, achieving and sustaining 91% BPA removal after 10 rounds of cyclic degradation. Reusability performance, composite resilience, apparent quantum yields, and figures of merit suggest that SSM@NiO/TiO₂ has excellent utility for practical applications.

Microwave-Assisted Synthesis of Zn2SnO4 Nanostructures for Photodegradation of Rhodamine B under UV and Sunlight

The contamination of water resources by pollutants resulting from human activities represents a major concern nowadays. One promising alternative to solve this problem is the photocatalytic process, which has demonstrated very promising and efficient results. Oxide nanostructures are interesting alternatives for these applications since they present wide band gaps and high surface areas. Among the photocatalytic oxide nanostructures, zinc tin oxide (ZTO) presents itself as an eco-friendly alternative since its composition includes abundant and non-toxic zinc and tin, instead of critical elements. Moreover, ZTO nanostructures have a multiplicity of structures and morphologies possible to be obtained through low-cost solution-based syntheses. In this context, the current work presents an optimization of ZTO nanostructures (polyhedrons, nanoplates, and nanoparticles) obtained by microwave irradiation-assisted hydrothermal synthesis, toward photocatalytic applications. The nanostructures’ photocatalytic activity in the degradation of rhodamine B under both ultraviolet (UV) irradiation and natural sunlight was evaluated. Among the various morphologies, ZTO nanoparticles revealed the best performance, with degradation > 90% being achieved in 60 min under UV irradiation and in 90 min under natural sunlight. The eco-friendly production process and the demonstrated ability of these nanostructures to be used in various water decontamination processes reinforces their sustainability and the role they can play in a circular economy.

Strategies to Enhance ZnO Photocatalyst's Performance for Water Treatment: A Comprehensive Review

Despite the photocatalytic organic pollutant degradation using ZnO started in 1910-1911, many challenges are still ahead, and several critical issues have to be addressed. Large band gap, and short life-time of photogenerated electrons and holes are critical issues negatively affect the photocatalytic activity of ZnO. Various approaches have been introduced to overcome these issues including intrinsic doping, extrinsic doping, and heterostructure. This review introduces unique and deep insights into tuning of the photocatalytic activity of ZnO. It starts by description of how to tune the photocatalytic activity of pristine ZnO through tuning its morphology, surface area, exposed face, and intrinsic defects. Afterward, the review explains how the Z-scheme approach succeed to address the redox weakened issue of heterojunction approach. In general, this review provides a clear image that helps the researcher to tune the photocatalytic activity of pristine ZnO and its heterostructure.

Sunlight-driven activation of peroxymonosulfate by microwave synthesized ternary MoO3/Bi2O3/g-C3N4 heterostructures for boosting tetracycline hydrochloride degradation

Design of direct Z-scheme heterojunction photocatalyst is considered as an effective strategy to fully use the high redox potential photogenerated charge carriers. This work reports a novel method for investigating the photosynergistic performance of the Z-scheme MoO₃/Bi₂O₃/g-C₃N₄ (MBG) photocatalyst with peroxymonosulfate (PMS) for the solar degradation of tetracycline hydrochloride (TCH), a model of organic pollutants in wastewater. The results showed a better strategy to activate PMS via accelerating the redox cycle (Mo⁶⁺/Mo⁵⁺), which ultimately induces the successive generation of highly reactive oxygen species. The effect of dosage of the catalyst, PMS, pH of the solution, initial concentrations of TCH and the presence of inorganic anions were investigated. It was found that the degradation of the TCH under sunlight irradiation (SL) was strongly enhanced by the presence of the PMS as an electron acceptor. The MBG/PMS/SL system was able to degrade an initial concentration (40 mg/L) of the TCH solution within 140 min. The good reusability and stability of the MBG catalyst were evaluated by recycling the degradation experiment. The main free radicals are OH and SO₄^─ which played an important role in the degradation reaction were identified by scavenger experiments and confirmed by EPR spectroscopy. X-ray photoelectron spectroscopy (XPS) study revealed the role of molybdenum ion in the activation process of PMS. The possible synergistic degradation reaction mechanism was proposed.

2D g-C3N4 as a bifunctional photocatalyst for co-catalyst and sacrificial agent-free photocatalytic N2 fixation and dye photodegradation

Photocatalytic N₂ fixation is an ecofriendly technology to produce ammonia.

Non-noble metallic Cu with three different roles in a Cu doped ZnO/Cu/g-C3N4 heterostructure for enhanced Z-scheme photocatalytic activity

Cu serves as a co-catalyst, an electron mediator, and a dopant leading to a high enhancement in the photocatalytic activity of Cu-ZnO/Cu/g-C₃N₄ Z-scheme photocatalyst.

Hybridized 2D Nanomaterials Toward Highly Efficient Photocatalysis for Degrading Pollutants: Current Status and Future Perspectives

Organic pollutants including industrial dyes and chemicals and agricultural waste have become a major environmental issue in recent years. As an alternative to simple adsorption, photocatalytic decontamination is an efficient and energy-saving technology to eliminate these pollutants from water environment, utilizing the energy of external light, and unique function of photocatalysts. Having a large specific surface area, numerous active sites, and varied band structures, 2D nanosheets have exhibited promising applications as an efficient photocatalyst for degrading organic pollutants, particularly hybridization with other functional components. The novel hybridization of 2D nanomaterials with various functional species is summarized systematically with emphasis on their enhanced photocatalytic activities and outstanding performances in environmental remediation. First, the mechanism of photocatalytic degradation is given for discussing the advantages/shortcomings of regular 2D materials and identifying the importance of constructing hybrid 2D photocatalysts. An overview of several types of intensively investigated 2D nanomaterials (i.e., graphene, g-C₃ N₄ , MoS₂ , WO₃ , Bi₂ O₃ , and BiOX) is then given to indicate their hybridized methodologies, synergistic effect, and improved applications in decontamination of organic dyes and other pollutants. Finally, future research directions are rationally suggested based on the current challenges.