Experimental and computational study of metal oxide nanoparticles for the photocatalytic degradation of organic pollutants: a review

Thermally synthesized hematite (α-Fe2O3) nanoparticles as efficient photocatalyst for visible light dye degradation

In recent years, water pollution has become a pressing global issue because of the continuous release of organic dyes from various industries. Therefore, finding an easy way to remove these harmful dyes from water has drawn the attention of researchers. This study investigates the removal of toxic Rose Bengal (RB) dye using hematite nanoparticles as a visible light photocatalyst without any additive. It is observed that by controlling particle size, quantity of the nanoparticles and reaction temperature, the dye degradation can be improved up to 95.33% with a half-life of 26 min. To understand photodegradation kinetic behavior, the Langmuir-Hinshelwood kinetic equation can be employed. The scavenger test indicated that the OH* radicals majorly led to the photodegradation process. The reaction rate values strongly depended on the size, quantity of the nanoparticles and reaction temperature. Controlling the optimizing condition, faster reaction rate (k = 0.027 min-1) can be achieved as compared to earlier reports. It is also noted that the change in the degradation efficiency of the reused catalyst is negligible when compared to the fresh one. Here, the dye degradation mechanism is discussed. Overall, this study reveals that hematite nanoparticles can be used as efficient photocatalyst for dye degradation applications by optimizing the controlling factors. These observations provide novel perspectives on the development of effective and sustainable photocatalytic technologies for pollution control and water treatment applications.

Exploring structural and optical properties of iodine-doped TiO2 nanoparticles in Rhodamine-B dye degradation: Experimental and theoretical investigation

Energy conversion and pollutant degradation are critical for advancing sustainable technologies, yet they often encounter challenges related to charge recombination and efficiency limitations. This study explores iodine-doped TiO2 nanoparticles as a potential solution for enhancing both energy conversion and pollutant degradation. The nanoparticles were synthesized via the sol-gel method with varying iodine precursor concentrations (0.025-0.1 M) and were characterized for their structural, compositional, and optical properties, particularly in relation to their photocatalytic performance in Rhodamine-B dye degradation. X-ray diffraction confirmed a tetragonal anatase crystal structure, with the average crystallite size decreasing from 10.06 nm to 8.82 nm with increase in iodine concentration. Selected area electron diffraction patterns verified the polycrystalline nature of the nanoparticles. Dynamic light scattering analysis showed hydrodynamic radii ranging from 95 to 125 nm. Fourier-transform infrared spectroscopy identified metal-oxygen vibrations at 441 cm⁻1, and electron microscopy confirmed the spherical morphology of the nanoparticles. Elemental analysis detected the presence of Ti, O, and I in the samples. Diffuse reflectance spectroscopy indicated the optical absorption edges for the doped samples in the visible region from which the corresponding band gap values were deduced. Photoluminescence spectroscopy revealed that the sample with 0.1 M iodine exhibit the lowest emission intensity, suggesting reduced charge recombination. Notably, 0.1 M iodine doped TiO2 samples demonstrated the highest photocatalytic efficiency, achieving 82.36% degradation of Rhodamine-B dye within 140 min under visible light. Additionally, ab-initio density functional theory calculations were performed to investigate the structural, optical, and adsorption properties of TiO2, iodine-doped TiO2, Rhodamine-B, and their composites, providing further insight into the enhanced photocatalytic activity observed in the experiments.

Three CoS/CoO microspheres and their mixed matrix membranes for the highly efficient photocatalytic degradation of methyl blue

Photocatalytic degradation technology, as one of the most important advanced oxidation technologies for environmental remediation, has attracted great attention in recent years, but designing photocatalysts with excellent photocatalytic activity and good reusability remains a challenge. Herein, three CoS/CoO microspheres (CoS/CoO-M-1 (1), CoS/CoO-M-2 (2), and CoS/CoO-M-3 (3)) were prepared via a hydrothermal method using cobalt chloride hexahydrate, thiourea, deionized water and polyethylene glycol (PEG) with different polymerization degrees as raw materials, which have a uniform size distribution in the range of 5-24 μm and specific surface areas of 6.1924 m2 g-1 (1), 6.2870 m2 g-1 (2) and 6.6663 m2 g-1 (3). It is worth noting that all the three CoS/CoO microspheres showed a wide optical absorption range from the ultraviolet to the near-infrared (NIR) region and a high photocatalytic activity for degrading methyl blue under visible light (500 W metal halide lamp) irradiation. In order to improve the portability and recyclability of 3, a mixed matrix membrane (MMM) of 3 (3-MMM) was manufactured by coating a mixture dispersion of 3 and polyvinylidene fluoride (PVDF) on a glass substrate, which not only displayed excellent photocatalytic degradation performance, but also showed good portability and reusability (cycles > 12 times). Furthermore, adsorption and photocatalytic kinetics and possible mechanisms were studied.

Earth-Abundant Recyclable Magnetic Iron Oxide Nanoparticles for Green-light Mediated C-H Arylation in Heterogeneous Phase

A magnetically isolable iron oxide nanoparticles is introduced as an efficient heterogeneous photocatalyst for non-directed C-H arylation employing aryl diazonium salts as the aryl precursors. This first-row transition metal-based photocatalyst revealed versatile activities and is applicable to a wide range of substrates, demonstrating brilliant efficacy and superior recyclability. Detailed catalytic characterization describes the physical properties and redox behavior of the Fe-catalyst. Adequate control experiments helped to establish the radical-based mechanism for the C-H arylation.

A Review of Plant-Mediated ZnO Nanoparticles for Photodegradation and Antibacterial Applications

This review focuses on the synthesis of plant-mediated zinc oxide nanoparticles (ZnO NPs) and their applications for antibacterial and photocatalytic degradation of dyes, thereby addressing the need for sustainable and eco-friendly methods for the preparation of NPs. Driven by the significant rise in antibiotic resistance and environmental pollution from dye pollution, there is a need for more effective antibacterial agents and photocatalysts. Therefore, this review explores the synthesis of plant-mediated ZnO NPs, and the influence of reaction parameters such as pH, annealing temperature, plant extract concentration, etc. Additionally, it also looks at the application of plant-mediated ZnO NPs for antibacterial and photodegradation of dyes, focusing on the influence of the properties of the plant-mediated ZnO NPs such as size, shape, and bandgap on the antibacterial and photocatalytic activity. The findings suggest that properties such as shape and size are influenced by reaction parameters and these properties also influence the antibacterial and photocatalytic activity of plant-mediated ZnO NPs. This review concludes that plant-mediated ZnO NPs have the potential to advance green and sustainable materials in antibacterial and photocatalysis applications.

TiO2 nanorod decorated with MoS2 nanospheres: An efficient dual-functional photocatalyst for antibiotic degradation and hydrogen production

The design and preparation of dual-functional photocatalysts for simultaneously realizing photocatalytic wastewater purification and hydrogen energy generation pose significant challenges. This article presents the engineering of a binary heterostructured photocatalyst by combining TiO2 (nanorods) and MoS2 nanosphere using a straightforward solvothermal method and the assessment of the phase structures, morphologies, and optical properties of the resulting nanocomposites using diverse analytical techniques. The TiO2(Rod)/MoS2 composite exhibits remarkable efficacy in degrading ciprofloxacin, achieving 93% removal rate within 1 h, which is four times higher than that of bare TiO2. Moreover, the optimized TiO2(Rod)/MoS2 presents an outstanding hydrogen production rate of 7415 μmol g-1, which is ∼24 times higher than that of pristine TiO2. Under UV-visible light irradiation, the TiO2(Rod)/MoS2 heterojunction displays an exceptional photocatalytic performance in terms of both photodegradation and hydrogen production, surpassing the performance of TiO2 particle/MoS2. The study findings demonstrate that TiO2(Rod)/MoS2 nanocomposites exhibit considerably improved photocatalytic degradation and hydrogen generation activities. Based on the experimental results, a possible mechanism is proposed for the transfer and separation of charge carriers in Z-scheme heterojunctions.

Er-Doped BiVO4/BiFeO3 Nanocomposites Synthesized via Sonochemical Process and Their Piezo-Photocatalytic Application

In this work, Er-doped BiVO4/BiFeO3 composites are prepared using the sonochemical process with a difference of rare earth loading compositions. The crystallinity and chemical and morphological structure of as-synthesized samples were investigated via X-ray diffraction, Raman scattering, and electron microscopy, respectively. The diffuse reflectance technique was used to extract the optical property and calculate the optical band gap of the composite sample. The piezo-photocatalytic performance was evaluated according to the decomposition of a Rhodamine B organic compound. The decomposition of the organic compound was achieved under ultrasonic bath irradiation combined with light exposure. The Er-doped BiVO4/BiFeO3 composite heterojunction material exhibited significant enhancement of the piezo-photocatalytic activity under both ultrasonic and light irradiation due to the improvement in charge generation and separation. The result indicates that Er dopant strongly affects the phase transformation, change in morphology, and alternation in optical band gap of the BiVO4 matrix. The incorporation of BiFeO3 in the composite form with BiVO4 doped with 1%Er can improve the photocatalytic performance of BiVO4 via piezo-induced charge separation and charge recombination retardment.

Green route to fabrication of Semal-ZnO nanoparticles for efficient solar-driven catalysis of noxious dyes in diverse aquatic environments

This work successfully demonstrates a sustainable and environmentally friendly approach for synthesizing Semal-ZnO nanoparticles (NPs) using the aqueous leaf extract of Bombax ceiba L. These NPs exhibit an absorption peak at approximately 390 nm in the UV-visible spectrum and an energy gap (Eg) of 3.11 eV. Detailed analyses of the morphology and particle size using various spectroscopic and microscopic techniques, XRD, FE-SEM with EDS, and HR-TEM reveal crystallographic peaks attributable to the hexagonal phase, with an average crystal size of 17 nm. The Semal-ZnO NPs also exhibit a notable photocatalytic efficiency for degrading methylene blue (MB) and methyl orange (MO) under sunlight in different water samples collected from diverse natural sources, indicating that they are promising photocatalysts for environmental remediation. The photocatalytic efficiency of the biofabricated Semal-ZnO NPs is impressive, exhibiting a photodegradation rate of up to 99% for MB and 79% for MO in different water samples under exposure to sunlight. The novel phytofabricated Semal-ZnO NPs are thus a beacon of hope for the environment, with their desirable photocatalytic efficiency, pseudo-first-order kinetics, and ability to break down noxious dye pollutants in various aquatic environments.

Vacancy induced enhanced photocatalytic activity of nitrogen doped CuO NPs synthesized by Co-precipitation method

The chemical co-precipitation method, an effective approach in the synthesis of nanomaterials, was used to synthesize CuO nanoparticles (NPs). Structural and morphological modification of undoped and nitrogen (N) doped CuO nanoparticles were studied thoroughly using X-ray diffraction (XRD), FT-IR and field emission scanning electron microscope (FE SEM). Doping effect on defects was investigated using X-ray photoelectron spectroscopy (XPS), Raman spectroscopy and photoluminescence (PL) spectroscopy. Thus, the effect of doping on crystallinity, crystallite size, strain induced in lattice, defects and electron-hole recombination rate were investigated. Optical band gap was calculated using Kubelka-Munk function from the diffuse reflectance spectra (DRS) obtained using ultraviolet visible (UV-Vis) spectroscopy. Finally, photocatalytic performance was studied from rhodamine B (Rh B) degradation and reaction kinetics were analyzed. Maximum degradation efficiency was obtained for 1.0 mol% N doped CuO NPs which also exhibited minimum band gap and lowest electron-hole recombination rate. For the optimum doping concentration, nitrogen was found to create oxygen vacancies while substituting oxygen in the lattice, and thus reduce electron-hole recombination rate and increase photocatalytic degradation rate effectively.

Graphene oxide as an emerging sole adsorbent and photocatalyst: Chemistry of synthesis and tailoring properties for removal of emerging contaminants

Contaminants of emerging concern (CEC) contain a wide range of compounds, such as pharmaceutical waste, pesticides, herbicides, industrial chemicals, organic dyes, etc. Their presence in the surrounding has extensive and multifaceted effects on human health as they have the potential to persist in the environment, accumulate in biota, and disrupt ecosystems. In this regard, various remediation methods involving different kind of functional nanomaterials with unique properties have been developed. The functional nanomaterials can provide several mechanisms for water pollutant removal, such as adsorption, catalysis, and disinfection, in a single platform. Graphene oxide (GO) is a two-dimensional carbon-based material that has an extremely large surface area and a large number of active sites. Recent advances in synthesising GO have shown great progress in tailoring its various physiochemical, optical, surface, structural properties etc., making it better adsorbent and photocatalysts. In this review, sole adsorbent and standalone photocatalytic performances of GO for the removal of CEC have been discussed in light of tailoring its adsorption and photocatalytic properties through novel synthesis routes and optimizing synthesis parameters. This review also examines various models describing the structure of GO and its surface/structural modifications for improved adsorption and photocatalytic properties. The article provides valuable information for the production of efficient and cost-effective GO-based sole adsorbents and photocatalysts as compared to the traditional materials. Furthermore, future prospective and challenges for sole GO nanostructures to compete with traditional adsorbents and photocatalysts have been discussed providing interesting avenues for future research.

Adsorption of cationic/anionic dyes and endocrine disruptors by yeast/cyclodextrin polymer composites

Factory and natural wastewaters contain a wide range of organic pollutants. Therefore, multifunctional adsorbents must be developed that can purify wastewater. Phytic acid-cross-linked Baker's yeast cyclodextrin polymer composites (IBY-PA-CDP) were prepared using a one-pot method. IBY-PA-CDP was used to adsorb methylene blue (MB), bisphenol A (BPA), and methyl orange (MO). Studies on the ionic strength and strongly acidic ion salts confirmed that IBY-PA-CDP adsorbs MO through hydrophobic interactions. This also shows that Na+ was the direct cause of the increased MO removal. Adsorption studies on binary systems showed that MB/MO inhibited the adsorption of BPA by IBY-PA-CDP. The presence of MB increased the removal rate of MO by IBY-PA-CDP due to the bridging effect. The Langmuir isotherm model calculated the maximum adsorption capacities for MB and BPA to be 630.96 and 83.31 mg g-1, respectively. However, the Freundlich model is more suitable for fitting the experimental data for MO adsorption. To understand the rate-limiting stage of adsorption, a mass-transfer mechanism model was employed. The fitting results show that adsorption onto the active sites is the rate-determining step. After five regeneration cycles, IBY-PA-CDP could be reused with good stability and recyclability.

Toxicity of Metal Oxides, Dyes, and Dissolved Organic Matter in Water: Implications for the Environment and Human Health

This study delves into the critical issue of water pollution caused by the presence of metal oxides, synthetic dyes, and dissolved organic matter, shedding light on their potential ramifications for both the environment and human health. Metal oxides, ubiquitous in industrial processes and consumer products, are known to leach into water bodies, posing a significant threat to aquatic ecosystems. Additionally, synthetic dyes, extensively used in various industries, can persist in water systems and exhibit complex chemical behavior. This review provides a comprehensive examination of the toxicity associated with metal oxides, synthetic dyes, and dissolved organic matter in water systems. We delve into the sources and environmental fate of these contaminants, highlighting their prevalence in natural water bodies and wastewater effluents. The study highlights the multifaceted impacts of them on human health and aquatic ecosystems, encompassing effects on microbial communities, aquatic flora and fauna, and the overall ecological balance. The novelty of this review lies in its unique presentation, focusing on the toxicity of metal oxides, dyes, and dissolved organic matter. This approach aims to facilitate the accessibility of results for readers, providing a streamlined and clear understanding of the reported findings.

The current status of hydrogen energy: an overview

Hydrogen is the most environmentally friendly and cleanest fuel that has the potential to supply most of the world's energy in the future, replacing the present fossil fuel-based energy infrastructure. Hydrogen is expected to solve the problem of energy shortages in the near future, especially in complex geographical areas (hills, arid plateaus, etc.) and harsh climates (desert, ice, etc.). Thus, in this report, we present a current status of achievable hydrogen fuel based on various scopes, including production methods, storage and transportation techniques, the global market, and the future outlook. Its objectives include analyzing the effectiveness of various hydrogen generation processes and their effects on the economy, society, and environment. These techniques are contrasted in terms of their effects on the environment, manufacturing costs, energy use, and energy efficiency. In addition, hydrogen energy market trends over the next decade are also discussed. According to numerous encouraging recent advancements in the field, this review offers an overview of hydrogen as the ideal renewable energy for the future society, its production methods, the most recent storage technologies, and transportation strategies, which suggest a potential breakthrough towards a hydrogen economy. All these changes show that this is really a profound revolution in the development process of human society and has been assessed as having the same significance as the previous industrial revolution.