Visible light driven exotic p (CuO) - n (TiO2) heterojunction for the photodegradation of 4-chlorophenol and antibacterial activity

Improved anti-diabetic and anticancer activities of green synthesized CuO nanoparticles derived from Tabernaemontana divaricate leaf extract

Copper oxide nanoparticles (CuO NPs) are among the most commonly employed nanoparticle materials owing to their antibacterial qualities, although their primary mechanism of action (MOA) is still not completely understood. CuO NPs are synthesized in this study using leaf extract of Tabernaemontana divaricate (TDCO3), and they are then analyzed using XRD, FT-IR, SEM, and EDX analysis. The zone of inhibition of TDCO3 NPs against both gram-positive (G+) B. subtilis and gram-negative (G-) K. pneumoniae bacteria was 34 mm and 33 mm, respectively. Furthermore, Cu2+/Cu+ ions promote reactive oxygen species and electrostatically bind with the negatively charged teichoic acid in the bacterial cell wall. The anti-inflammatory and anti-diabetics analysis was conducted using standard BSA denaturation and α-amylase inhibition technique with cell inhibition values of 85.66 and 81.18% for TDCO3 NPs. Additionally, the TDCO3 NPs delivered prominent anticancer activity with the lowest IC50 value 18.2 μg/mL in the MTT assay technique against HeLa cancer cells.

A Review of Synthesis Methods, Modifications, and Mechanisms of ZnO/TiO2-Based Photocatalysts for Photodegradation of Contaminants

The environment being surrounded by accumulated durable waste organic compounds has become a critical crisis for human societies. Generally, organic effluents of industrial plants released into the water source and air are removed by some physical and chemical processes. Utilizing photocatalysts as cost-effective, accessible, thermally/mechanically stable, nontoxic, reusable, and powerful UV-absorber compounds creates a new gateway toward the removal of dissolved, suspended, and gaseous pollutants even in trace amounts. TiO2 and ZnO are two prevalent photocatalysts in the field of removing contaminants from wastewater and air. Structural modification of the photocatalysts with metals, nonmetals, metal ions, and other semiconductors reduces the band gap energy and agglomeration and increases the affinity toward organic compounds in the composite structures to expand their usability on an industrial scale. This increases the extent of light absorbance and improves the photocatalytic efficiency. Selecting a suitable synthesis method is necessary to prepare a target photocatalyst with distinct properties such as high specific surface area, numerous surface functional groups, and an appropriate crystalline phase. In this Review, significant parameters for the synthesis and modification of TiO2- and ZnO-based photocatalysts are discussed in detail. Several proposed mechanistic routes according to photocatalytic composite structures are provided. Some electrochemical analyses using charge carrier trapping agents and delayed recombination help to plot mechanistic routes according to the direction of photoexcited species (electron-hole pairs) and design more effective photocatalytic processes in terms of cost-effective photocatalysts, saving time and increasing productivity.

Gas-Phase Fabrication and Photocatalytic Activity of TiO2 and TiO2-CuO Nanoparticulate Thin Films

CuO-loaded TiO2 nanomaterials have applications in pollutant degradation via photocatalysis. However, the existing methods of fabricating these nanomaterials involve liquid-phase processes, which require several steps and typically generate liquid waste. In this study, TiO2 and TiO2-CuO nanoparticulate thin films were successfully fabricated through a one-step gas-phase approach involving a combination of plasma-enhanced chemical vapor deposition and physical vapor deposition. The resulting films consisted of small, spherical TiO2 nanoparticles with observable CuO on the TiO2 surface. Upon annealing in air, the TiO2 nanoparticles were crystallized, and CuO was completely oxidized. The photocatalytic activity of TiO2-CuO/H2O2, when introduced into the rhodamine 6G degradation system, was substantially enhanced under both ultraviolet and visible light irradiation. Moreover, this study highlights the influence of pH on the photocatalytic activity; TiO2-CuO/H2O2 exhibited the highest photocatalytic activity at pH 13, with a reaction rate constant of 0.99 h-1 cm-2 after 180 min of visible light irradiation. These findings could facilitate the development of nanoparticulate thin films for enhanced pollutant degradation in wastewater treatment.

Biochar supported nano core-shell (TiO2/CoFe2O4) for wastewater treatment

The porous structure of biochar, its large surface area, and its anti-oxidant properties are extensively used for pollutant removal strategies. The literature to date has reported that the biochar assisted metal-oxide core-shells have a dominating degradation ability under solar irradiation. Therefore, this study is significantly focused on cinnamon biochar as an active anti-oxidant agent incorporated in titania-cobalt ferrite nanocore-shell (Biochar/TiO2/CoFe2O4) structures for the first time in wastewater treatment against chlorophenol pollutants. Pure materials, core-shells, and biochar aided composites were synthesized by chemical methods, and their characteristics were analyzed using various instrumentation techniques. The diffraction outcomes of Biochar/TiO2/CoFe2O4 showed the mixed phases containing biochar, TiO2, and CoFe2O4. The morphological characteristics revealed that the biochar creates porosity and a peripheral layer covering the core-shell. Meanwhile, absorption studies of TiO2/CoFe2O4 core-shell and Biochar/TiO2/CoFe2O4 samples achieved 65% and 92% degradation efficiencies when exposed to visible light against chlorophenol pollutants, respectively. All these results confirm the presence of distinct functional groups as well as the combined synergistic effects that activated the charge separation, resulting in the successful destruction of water pollutants. In addition, the highly efficient Biochar/TiO2/CoFe2O4 sample was recycled, and the efficiency was maintained stable for five repeated degradation processes. Thus, Biochar/TiO2/CoFe2O4 will be utilized to expand the possibilities for biofuel generation and energy storage devices.

The degradation of bisphenol-A organic pollutant using the dispersal of TiO2 nanorods onto the partial reduction of graphene oxide nanosheets

The notion of innovative combinations of semiconducting metal oxides for photocatalytic destruction is a key factor in the removal of environmental contaminants. However, for the first time, the combination was made possible for the aforementioned reason by embedding one-dimensional titanium dioxide (TiO2) semiconductor nanorods on two-dimensional rGO (reduced graphene oxide) nanosheets utilizing hydrothermal and a modified Hummers' method. By applying several sophisticated procedures, the properties of these catalysts were found, and then the degradation of BPA (bisphenol-A) was examined with UV and visible light sources. Further, all the analyses were performed on pure TiO2 material. As a result of the synergistic interaction between TiO2 and rGO, the rGO-TiO2 catalyst produced a favorable photocatalytic outcome. The structural investigation of rGO-TiO2 has confirmed that the TiO2 was in anatase phase along with GO and rGO peaks, and the morphological characterization showed that the TiO2 nanorods were integrated randomly into the rGO nanosheets along with defective sites. Also, adding rGO to TiO2 causes charge separation, and π-π interactions to improve the visible light absorption range. In this study, the main model organic component in the photocatalytic degradation is bisphenol-A (BPA). During visible light irradiation, the OH radicals were finally produced by the redox reactions. Furthermore, the rGO surface adsorbs the phenol molecules due to graphene π-π interactions, thus narrowing the band gap and increasing the efficiency of BPA degradation.

Recent advances of semiconductor photocatalysis for water pollutant treatment: mechanisms, materials and applications

Semiconductor photocatalysis has become an increasing area of interest for use in water treatment methods. This review systematically presents the recent developments of emerging semiconductor photocatalysis system and their application in the removal of water pollutants. A brief overview of the semiconductor photocatalysis mechanism involved with the generation of reactive oxygen species (ROS) is provided first. Then a detailed explanation of the development of TiO2-based, g-C3N4-based, and bismuth-based semiconductor materials and their applications in the degradation of water pollutants are highlighted with recent illustrative examples. Furthermore, the future prospects of semiconductor photocatalysis for water treatment are critically analyzed.

Engineering cuboctahedral N-doped C-coated p-CuO/n-TiO2 heterojunctions toward high-performance photocatalytic cross-dehydrogenative coupling

The low separation efficiency of photogenerated electron-hole (e-h) pairs severely limits the activation of photocatalyts. One brilliant strategy is to construct a p-n type semiconductor heterojunction, which can establish an inner electric field to separate the e-h pairs with high efficiency. Here, for the first time, a cuboctahedral N-doped carbon-coated CuO/TiO2 p-n heterojunction (CuO-TiO2@N-C) was designed and fabricated successfully via direct calcination of a benzimidazole-modulated cuboctahedral HKUST-Cu with titanium-tetraisopropanolate absorbed inside concomitantly. Full structural characterizations incorporating DFT computations demonstrate that the CuO/TiO2 p-n heterostructure can greatly boost the transport and separation of photoinduced e-h pairs. The nitrogen-doped carbon coating, with its excellent conductivity, porosity, stability and surface reaction activity, plays a pivotal role in promoting the overall performance and effectiveness of the reaction. The CuO-TiO2@N-C displays significantly higher photocurrent density (0.042 μA cm-2) than the CuO@N-C (0.014 μA cm-2) and TiO2@N-C (0.03 μA cm-2) electrodes, proving that the p-n heterojunction can improve the e-h generation efficiency. This unique photocatalyst affords superior photocatalytic efficiency, cycle stability and substrate scope towards cross-dehydrogenative coupling reactions.

Degradation of 2,4-diclorophenol via coupling zero valent iron and hydrodynamic cavitation for sulfite activation: A turbulence modeling

The 2,4-dichlorophenol (2,4-DCP) is an important chemical precursor that can affect human endocrine system and induce pathological symptoms. This research reports the degradation of 2,4-DCP using lab-scale hydrodynamic cavitation (HC) approach, which is considered a green and effective method. To promote the degradation efficiency, the zero-valent iron (Fe⁰) as the catalyst for sulfate radical (SO₄^•-) generation via activation of sulfite (SO₃^2-) salts was simultaneously used. Degradation efficiency was favorable in acidic pH than the alkaline pH due to higher production of active radicals and was dependent on the dose of Fe⁰ and SO₃^2-. Under optimal condition, degradation efficiency by Fe⁰/HC/sulfite (96.67 ± 2.90%) was considerably enhanced compared to HC alone (45.37 ± 2.26%). Quenching experiments suggested that SO₄^•-, ^•OH, ¹O₂, and O₂^•- radicals were involved in the degradation of 2,4-DCP by Fe⁰/HC/sulfite process, but the dominant role was related to ^•OH (70.09% contribution) and SO₄^•- (29.91% contribution) radicals. From the turbulence model, turbulent pressure at venturi throat decreased from -0.42 MPa to -2.02 MPa by increasing the inlet pressure from 1.0 to 4.0 bar and increase in pressure gradient has intensified bubble collapse due to higher turbulence tension.

Eco-friendly cubic-ZnS coupled Cu7S4 spines on chitosan matrix: Unravelling defect-engineered nanoplatform for the photodegradation of p-chlorophenol

Novel ZnS-Cu₇S₄ nanohybrid supported on chitosan matrix, as an ideal photocatalyst, was fabricated by the sonochemical method wherein high-resolution transmission electron microscopy (HRTEM) and X-ray powder diffraction (XRD) analysis confirmed the co-existence of both ZnS and Cu₇S₄; presence of vacancy sites in ZnS was verified by electron paramagnetic resonance (EPR) analysis and their introduction could promote two-photon excitation facilitated visible light response and charge transport/separation. The type II interface is formed in the ZnS-Cu₇S₄/Chitosan heterojunction owing to interstitial states that promote charge separation. The ZnS-Cu₇S₄/Chitosan was used for the photodegradation of a pharmaceutical pollutant, p-chlorophenol (PCP); over 98.8% of PCP photodegradation was achieved under visible-light irradiation where the ensued ·O₂^- and ·OH serve a key role in the photodegradation of PCP. In vitro cytotoxicity studies substantiated that the ZnS-Cu₇S₄/Chitosan is nontoxic to the ecosystem and human beings and endowed with promising photodegradation properties and accessibility via an environmentally friendly design, bodes well for its potential remediation applications.

Green Synthesis of CuO-TiO2 Nanoparticles for the Degradation of Organic Pollutants: Physical, Optical and Electrochemical Properties

CuO-TiO2 nanocomposites were successfully synthesized using the C. benghalensis plant extracts. The effect of the composition of CuO to TiO2 on the morphological, optical, electrochemical, and photodegradation efficiency in the composites was studied. SEM, XRD, UV-vis, FTIR, TGA, BET, and CV were used to characterize these materials. The XRD data reported the tenorite structure of the CuO and the anatase phase of the TiO2. SEM showed the spherical morphologies for all the CuO-TiO2 NPs, and these were also mesoporous in nature, as depicted by BET. The voltammogram of the CuO-TiO2 30/70 electrode showed a higher response current density compared to the other two samples, suggesting a higher specific capacitance. Upon testing the photocatalytic efficiencies of the CuO-TiO2 nanocomposites against methylene blue (MB), ciprofloxacin (CIP), and sulfisoxazole (SSX), the highest degradation of 94% was recorded for SSX using the CuO-TiO2 30/70 nanocomposites. Hydroxyl radicals were the primary species responsible for the photodegradation of SSX, and the material could be reused once. The most active species in the photodegradation of SSX has been identified as OH•. From this study, it can be noted that the CuO-TiO2 nanocomposites were more selective toward the degradation of antibiotics (sulfisoxazole and ciproflaxin) as compared to dyes (methylene blue).

Direct Z-Scheme g-C3N5/Cu3TiO4 Heterojunction Enhanced Photocatalytic Performance of Chromene-3-Carbonitriles Synthesis under Visible Light Irradiation

In order to make the synthesis of pharmaceutically active carbonitriles efficient, environmentally friendly, and sustainable, the method is regularly examined. Here, we introduce a brand-new, very effective Cu3TiO4/g-C3N5 photocatalyst for the production of compounds containing chromene-3-carbonitriles. The direct Z-Scheme photo-generated charge transfer mechanism used by the Cu3TiO4/g-C3N5 photocatalyst results in a suppressed rate of electron-hole pair recombination and an increase in photocatalytic activity. Experiments showed that the current method has some advantages, such as using an environmentally friendly and sustainable photocatalyst, having a simple procedure, quick reaction times, a good product yield (82–94%), and being able to reuse the photocatalyst multiple times in a row without noticeably decreasing its photocatalytic performance.

New insight into the kinetic study on the different loadings of the CuO/CNT catalyst and its optimization for p-chloroaniline photodegradation

The effect of the copper (Cu) content on Cu oxide loaded onto a carbon nanotube (CuO/CNT) catalyst on the mechanistic, kinetic, and photonic efficiency of the photodegradation of p-chloroaniline (PCA) under visible (Vis) and ultraviolet (UV) light irradiation has been explored. For low-loading (1-5 wt%) CuO/CNTs, photodegradation performed better under UV (>84%) rather than the Vis system; this may be due to the presence of abundant defect sites on both CuO and CNTs, which allowed the multielectron reduction of oxygen at their impurity levels to generate more hydrogen peroxide and subsequent ·OH radicals. The active species under UV were in the following order: h⁺ ≫ e^- > ·OH, while it was vice versa for the Vis system with a well-balanced 50 wt% CuO/CNT catalyst that exhibited a similar performance. The kinetic study showed the transition of the kinetic order from the zeroth to the first order on increasing the PCA concentration under the Vis system and vice versa for the UV system. The Thiele modulus (ϕ) further confirmed that the effect of internal mass transfer was negligible under UV light. In contrast, the transition from mass transfer to kinetic control limitation was observed under the Vis system. The optimum PCA degradation predicted from the response surface analysis was 97.36% at the reaction pH of 7.3, catalyst dosage of 0.45 g L^-1, and initial PCA concentration of 11.02 mg L^-1. The condition obtained was fairly close to the forecasted value with an error of 0.26%.

Fabrication of ZnAl-LDH mixed metal-oxide composites for photocatalytic degradation of 4-chlorophenol

In this work, two different types of ZnAl-layered double hydroxide (LDH) mixed metal-oxide composites (CeO₂ and SnO₂) were synthesized and applied for the photodegradation of 4-chlorophenol (4-CP) in wastewater. The fabricated CeO₂/ZnAl-LDH and SnO₂/ZnAl-LDH were characterized by X-ray diffraction (XRD), Fourier transform infrared (FTIR) spectroscopy, UV-visible diffuse reflectance spectroscopy (UV-vis DRS), and theoretical density functional theory (DFT) calculations, suggesting that the band gaps of the synthesized hybrid composites were much lower than those of traditional ZnAl-LDH. In addition, the photocatalytic activity for 4-CP degradation and reaction kinetics were investigated to evaluate the catalytic behavior of the prepared composites. The results indicated that the photocatalytic process in this case followed a pseudo-first-order kinetic model, and SnO₂/ZnAl-LDH illustrated the optimum performance for 4-CP degradation with an efficiency of 95.2% due to its stability and recyclability. Additionally, the reaction mechanism of 4-CP photodegradation was studied over SnO₂/ZnAl-LDH; it presented that 4-CP could be oxidized by hydroxyl radicals, holes, and superoxide radicals, where hydroxyl radicals were identified as the dominant active species during the degradation process. Finally, decomposition intermediates were measured to deduce the reaction pathway of 4-CP, and three tentative pathways were proposed and discussed.

A review on self-modification of zirconium dioxide nanocatalysts with enhanced visible-light-driven photodegradation of organic pollutants

Over the past few years, photocatalysis is one of the most promising approaches for removing organic pollutants. Zirconium dioxide (ZrO₂) has been shown to be effective in the photodegradation of organic pollutants. However, low photoresponse and fast electron-hole recombination of ZrO₂ affected the efficiency of catalytic performance. Modifying the photocatalyst itself (self-modification) is a prominent way to enhance the photoactivity of ZrO₂. Moreover, as ZrO₂-like photocatalysts have a large bandgap, improving the spectral response via self-modification could extend the visible light region and reduce the chance of recombination. Here, we review the self-modification of ZrO₂ for enhanced the degradation of organic pollutants. The approaches of the ZrO₂ self-modification, including the type of synthetic route and synthesis parameter variation, are discussed in the review. This will be followed by a brief section on the effect of ZrO₂ self-modification in terms of morphology, crystal structure, and surface defects for enhanced photodegradation efficiency. It also covers the discussion on the photocatalytic mechanism of ZrO₂ self-modification. Finally, some challenges with ZrO₂ catalysts are also discussed to promote new ideas to improve photocatalytic performance.

Iron oxide (Fe3O4)-laden titanium carbide (Ti3C2Tx) MXene stacks for the efficient sequestration of cationic dyes from aqueous solution

We prepared two-dimensional (2D) stack-structured magnetic iron oxide (Fe₃O₄) nanoparticle anchored titanium carbide (Ti₃C₂T_x) MXene material (Ti₃C₂T_x/Fe₃O₄). It was used as a potential adsorbent to remove carcinogenic cationic dyes, such as methylene blue (MB) and rhodamine B (Rh B), from aqueous solutions. Ti₃C₂T_x/Fe₃O₄ exhibited maximum adsorption capacities of 153 and 86 mg g^-1 for MB and Rh B dyes, respectively. Batch adsorption experimental data fits the Langmuir model well, revealing monolayer adsorption of MB and Rh B onto the adsorption sites of Ti₃C₂T_x/Fe₃O₄. Additionally, Ti₃C₂T_x/Fe₃O₄ showed rapid MB/Rh B adsorption kinetics and attained equilibrium within 45 min. Moreover, Ti₃C₂T_x/Fe₃O₄ demonstrated recyclability over four cycles with high stability due to the presence of magnetic Fe₃O₄ nanoparticles. Furthermore, it exhibited remarkable selectivities of 91% and 88% in the presence of co-existing cationic and anionic dyes, respectively. Given the extraordinary adsorption capacities, Ti₃C₂T_x/Fe₃O₄ may be a promising material for the effective removal of cationic dyes from aqueous media.

Investigation of the Sn4+-distribution and photocatalytic performance of Sn4+/TiO2 hollow fiber nanomaterials

Tin ion-doped TiO2 fibers were smartly prepared, and the distribution depth of Sn4+ influences the photocatalytic performance of TiO2.