Enhanced photocatalytic activity of TiO2 by reduced graphene oxide in mineralization of Rhodamine B dye

Ag2O-adorned ZnO nanostructures: cooperative and sustainable nanomaterial system for effective reduction and mineralization of hazardous water pollutants

Organic water pollutants like nitroaromatics and synthetic dyes are causing serious threats to water. Ever-growing urban and industrial activities along with population explosion are rapidly contributing severe level of water contamination. Semiconducting nanomaterial-based photocatalysis has been proven to be an effective process for degradation of organic water pollutants. In the current study, visible light active Ag₂O-adorned ZnO nanostructures were fabricated by a simple two-step hydrothermal method and the prepared nanostructures were utilized for the photocatalytic mineralization of rhodamine B (RhB) dye with visible light radiation. The catalytic potential of as-synthesized nanostructures was also investigated for the reduction of nitroaromatics (4-NP and 4-NA) and RhB dye in the presence of NaBH₄. The Ag₂O-adorned ZnO nanostructures prepared with 5% of silver nitrate denoted as ZnO/Ag₂O (5%) demonstrated stupendous photomineralization activity against RhB dye as almost 100% degradation of RhB dye was achieved within 100 min of reaction time at pH = 6. The kinetic study revealed that the degradation reaction followed the pseudo-first-order kinetics and the kinetic rate constant (k) of photodecolorization reaction for optimal catalyst was calculated to be 61.4 × 10^-3 min^-1. The nanostructures revealed excellent recyclability and photostability as 95% activity of the catalyst was preserved even after the fifth cyclic run. The catalytic reduction of the 4-NP, 4-NA, and RhB dye was completed in 21, 12, and 40 min, respectively, in the presence of ZnO/Ag₂O (5%) and NaBH₄ solution. The kinetic rate constant values for the reduction reactions were determined to be 229.6 × 10^-3, 454.2 × 10^-3, and 105.5 × 10^-3 min^-1 for 4-NP, 4-NA, and RhB dye, respectively. Thus, the obtained results suggest that the components of the prepared nanosystem help in mutually strengthening the catalytic and photocatalytic abilities of each other, indicating the development of a cooperative and sustainable nanomaterial system in the current study.

Fabrication of an effectual, stable and reusable Mg-doped CdAl2O4 nanoparticles for photodegradation of toxic pollutants under visible light illumination

The water contamination caused by discharging extensive organic dyes stuff into water bodies is one of the utmost significant concerns disturbing the environment and human life. CdAl₂O₄ spinel materials have been excellent in the elimination of emerging pollutants by the photocatalysis route. These materials, when altered through methods namely doping with Mg ions, have benefits over CdAl₂O₄, especially reduced energy gap and light absorbed in the visible region. The XRD established the creation of space group R 3‾ with no other phase step being found. The photoluminescence outcomes indicated that Mg-doped CdAl₂O₄ nanoparticles had the preventing e^--h⁺ recombination possibility, which was favorable for the photocatalytic process. The Mg (0.075 M)-doped CdAl₂O₄ catalyst had higher photocatalytic performance with 94 and 96% removal of two azo (BB and BG) dyes under a mere 90 min visible light irradiation, which indicated enhanced Photodegradation behaviors when compared to other Mg (0.025, 0.050 M)-doped and pure CdAl₂O₄ materials. More interestingly, pH 5 was optimum for the Mg (0.075 M)-doped CdAl₂O₄ samples photodegradation of both dyes, and the optimum catalyst amount was 5 mg/100 mL. The doped Mg ions influenced the elimination of both dyes by inducing the manufacture of more active species. The Mg (0.075 M)-doped CdAl₂O₄ samples is reusable and highly stable with only a 5% reduction in degradation rate after six cycles. Based on the quencher and ESR investigations, the ^.OH^- and h⁺ are described as active species in the removal reaction. We hope our present examinations highlight the possibility of using Mg (0.075 M)-doped CdAl₂O₄ product for a broad range of photodegradation applications, also it may be applied for several ecological remediations, surface cleaning devices, foods and pharmaceutical industry applications.

Improved visible-light-driven photocatalytic removal of Bisphenol A using V2O5/WO3 decorated over Zeolite: Degradation mechanism and toxicity

WO₃/Zeolite/V₂O₅ (TZV) composite synthesized through co-precipitation was used for the degradation of Bisphenol-A (BpA). XRD and Raman spectra were employed to ascertain the crystallinity of the composite. The pristine nature of the compound without any free particles over the zeolite surface was established through FESEM, thus, substantiating the composite character of the material. The enhancement in activity after doping with WO₃ was ascertained by DRS-UV. Photocatalytic degradation studies clearly established the superiority of TZV 10 over bare V₂O₅. Complete BpA degradation (100%) was attained at 50 min of incubation with 0.75 g/L TZV-10 in acidic medium (pH 3) for an initial BpA concentration of 100 mg/L. HPLC-MS/MS analysis was used to decipher the degradation pathway. The catalyst was stable even after 9 cycles. Phytotoxicity studies and lake water treatment results proved the environmental efficiency of the synthesized material.

Synergistic effects of the hybridization between boron-doped carbon quantum dots and n/n-type g-C3N4 homojunction for boosted visible-light photocatalytic activity

Dye wastewater has raised a prevalent environmental concern due to its ability to prevent the penetration of sunlight through water, thereby causing a disruption to the aquatic ecosystem. Carbon quantum dots (CQDs) are particularly sought after for their highly tailorable photoelectrochemical and optical properties. Simultaneously, graphitic carbon nitride (g-C₃N₄) has gained widespread attention due to its suitable band gap energy as well as excellent chemical and thermal stabilities. Herein, a novel boron-doped CQD (BCQD)-hybridized g-C₃N₄ homojunction (CN) nanocomposite was fabricated via a facile hydrothermal route. The optimal photocatalyst sample, 1-BCQD/CN (with a 1:3 mass ratio of boron to CQD) accomplished a Rhodamine B (RhB, 10 mg/L) degradation efficiency of 96.8% within 4 h under an 18 W LED light irradiation. The kinetic rate constant of 1.39 × 10^-2 min^-1 achieved by the optimum sample was found to be 3.6- and 2.8-folds higher than that of pristine CN and un-doped CQD/CN, respectively. The surface morphology, crystalline structure, chemical composition and optical properties of photocatalyst samples were characterized via TEM, FESEM-EDX, XRD, FTIR, UV-Vis DRS and FL spectrometer. Based on the scavenging tests, it was revealed that the photogenerated holes (h⁺), superoxide anions (∙O₂^-) and hydroxyl radicals (∙OH) were the primary reactive species responsible for the photodegradation process. Overall, the highly efficient 1-BCQD/CN composite with excellent photocatalytic activity could provide a cost-effective and robust means to address the increasing concerns over global environmental pollution.

Visible-Light-Driven Reduced Graphite Oxide as a Metal-Free Catalyst for Degradation of Colored Wastewater

Reduced graphite oxide (rGO)-based materials have demonstrated promising potential for advanced oxidation processes. Along with its distinctive 2D characteristics, rGO offers the prospect of catalytic degradation of various kinds of organic pollutants from aqueous environments. The practical application of rGO as a metal-free catalyst material to promote the Fenton reaction depends on the degree of rGO reduction. In this regard, the rGO was prepared according to oxidation by modified Hummers' method and two-step reduction via hydrothermal and calcination in the N2 atmosphere. The as-prepared rGO was characterized in terms of X-ray diffraction, Fourier-transform infrared spectroscopy, thermal gravimetric analysis, scanning electron microscopy, UV-vis absorption spectroscopy, and transmission electron microscopy. The effectiveness of as-prepared rGO as a photocatalyst and the metal-free catalyst to decolorize different textile dyes, including basic red 46, basic red 18, and methylene blue, was investigated in visible/rGO and visible/rGO/H2O2 systems. The impact of operational factors such as catalyst dose, pH, and initial dye concentration was examined. The dye degradation process was investigated by the pseudo-first-order kinetic model. In addition, the recyclability of rGO in the visible/rGO/H2O2 system was examined.

Immobilised rGO/TiO2 Nanocomposite for Multi-Cycle Removal of Methylene Blue Dye from an Aqueous Medium

This work presents the immobilisation of titanium dioxide (TiO2) nanoparticles (NPs) and reduced graphene oxide (rGO)-TiO2 nanocomposite on glass sheets for photocatalytic degradation of methylene blue (MB) under different radiation sources such as ultraviolet and simulated solar radiation. The TiO2 NPs and rGO-TiO2 nanocomposite were synthesised through a simple hydrothermal method of titanium isopropoxide precursor followed by calcination treatment. Deposition of prepared photocatalysts was performed by spin-coating method. Additionally, ethylene glycol was mixed with the prepared TiO2 NPs and rGO-TiO2 nanocomposite to enhance film adhesion on the glass surface. The photocatalytic activity under ultraviolet and simulated solar irradiation was examined. Further, the influence of different water matrices (milli-Q, river, lake, and seawater) and reactive species (h+, •OH, and e−) on the photocatalytic efficiency of the immobilised rGO/TiO2 nanocomposite was careful assessed. MB dye photocatalytic degradation was found to increase with increasing irradiation time for both irradiation sources. The immobilisation of prepared photocatalysts is very convenient for environment applications, due to easy separation and reusability, and the investigated rGO/TiO2-coated glass sheets demonstrated high efficiency in removing MB dye from an aqueous medium during five consecutive cycles.

Enhanced Photocatalytic Activity of Hybrid rGO@TiO2/CN Nanocomposite for Organic Pollutant Degradation under Solar Light Irradiation

The three-component hybrid (rGO/TiO2/CN) nanocomposite was prepared in order to enhance the photocatalytic properties of anatase TiO2 nanoparticles (NPs) under solar-like irradiation. The rGO/TiO2/CN was prepared in a mixture of the reduced graphene oxide (rGO, 8 wt%), anatase TiO2 nanoparticles (NPs), and graphitic carbon nitride (g-C3N4, 16 wt%). It was self-assembled through the one-step hydrothermal method, followed by an annealing process. The photocatalyst was thoroughly characterized by means of X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), Fourier transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM), transmission electron microscopy (TEM), the Brunauer-Emmett-Teller (BET) nitrogen adsorption/desorption technique and UV-Vis diffuse reflectance spectroscopy (DRS). The photocatalytic activity of the TiO2, TiO2/rGO, TiO2/CN and hybrid rGO/TiO2/CN nanocomposite was studied through the degradation of a rhodamine B (RhB) aqueous solution under solar-like irradiation. The results showed that the highest photocatalytic activity was achieved by the rGO/TiO2/CN mixture, which can be attributed to the synergistic effect of the incorporation of both rGO and g-C3N4 with TiO2. Further, the influence of the pH value of the RhB dye aqueous solution and different water matrix (Milli-Q, tap, and alkaline water) on the photocatalytic efficiency of the rGO/TiO2/CN nanocomposite was examined. In addition, a recycle test was performed for hybrid rGO@TiO2/CN to investigate the effectiveness of the photodegradation of RhB dye in three successive cycles. The conducted results indicate that the pH value of RhB dye aqueous solution and water matrices play an important role in the photocatalytic degradation rate.

An Overview on Graphene-Metal Oxide Semiconductor Nanocomposite: A Promising Platform for Visible Light Photocatalytic Activity for the Treatment of Various Pollutants in Aqueous Medium

Graphene is one of the most favorite materials for materials science research owing to its distinctive chemical and physical properties, such as superior conductivity, extremely larger specific surface area, and good mechanical/chemical stability with the flexible monolayer structure. Graphene is considered as a supreme matrix and electron arbitrator of semiconductor nanoparticles for environmental pollution remediation. The present review looks at the recent progress on the graphene-based metal oxide and ternary composites for photocatalysis application, especially for the application of the environmental remediation. The challenges and perspectives of emerging graphene-based metal oxide nanocomposites for photocatalysis are also discussed.

Controllable synthesis of peapod-like TiO2@GO@C electrospun nanofiber membranes with enhanced mechanical properties and photocatalytic degradation abilities towards methylene blue

Electrospun peapod-like TiO₂@GO@C nanofiber membranes enhance their photocatalytic properties for the improved crystallinity of TiO₂ and carrier transport, and simultaneously improve their mechanical properties.

Enhanced photocatalytic degradation of methyl orange by porous graphene/ZnO nanocomposite

Degrading aquatic organic pollutants efficiently is very important but strongly relied on the design of photocatalysts. Porous graphene could increase photocatalytic performance of ZnO nanoparticles by promoting the effective charge separation of electron-hole pairs if they can be composited. Herein, porous graphene, ZnO nanoparticles and porous graphene/ZnO nanocomposite were prepared by fine tuning of partial combustion, which graphene oxide imperfectly covered by the layered Zn salt was combusted under muffle furnace within few minutes. Resulting ZnO nanoparticles (32-72 nm) are dispersed uniformly on the surface of graphene sheets, the pore sizes of porous graphene are in the range from ∼3 to ∼52 nm. The synthesized porous graphene/ZnO nanocomposite was confirmed to show enhanced efficiency under natural sunlight irradiation compared with pure ZnO nanoparticles. Using porous graphene/ZnO nanocomposite, 100% degradation of methyl orange can be achieved within 150 min. The synergetic effect of photocatalysis and adsorption is main reason for excellent MO degradation of PG/ZnO nanocomposite. This work may offer a new route to accurately prepare porous graphene-based nanocomposite and open a door of their applications.

Tungsten-doped TiO2/reduced Graphene Oxide nano-composite photocatalyst for degradation of phenol: A system to reduce surface and bulk electron-hole recombination

Recombination of photogenerated charges is the main factor affecting the photocatalytic activity of TiO₂. Here, we report a combined strategy of suppressing both the bulk as well as the surface recombination processes by doping TiO₂ with tungsten and forming a nanocomposite with reduced graphene oxide (rGO), respectively. Sol-gel method was used to dope and optimize the concentration of W in TiO₂ powder. UV-Vis, XPS, PL and time resolved PL spectra along with DFT calculations indicate that W⁶⁺ in TiO₂ lattice creates an impurity level just below the conduction band of TiO₂ to act as a trapping site of electrons, which causes to improve the lifetime of the photo-generated charges. Maximum reduction in the PL intensity and the improvement in charge carrier lifetime was observed for TiO₂ doped with 1 at.% W (1W-TiO₂), which also displayed the highest photo-activity for the degradation of p-nitro phenol pollutant in water. Tuning of rGO/TiO₂ ratio (weight) disclosed that the highest activity can be achieved with the composite formed by taking equal amounts of TiO₂ and rGO (1:1), in which the strong interaction between TiO₂ and rGO causes an effective charge transfer via bonds formed near the interface as indicated by XPS. Both these optimized concentrations were utilized to form the composite rGO/1W-TiO₂, which showed the highest activity in photo-degradation of p-nitro phenol (87%) as compared to rGO/TiO₂ (42%), 1W-TiO₂ (62%) and pure TiO₂ (29%) in 180 min. XPS and PL results revealed that in the present nanocomposite, tungsten species traps the excited electron to reduce the interband recombination in the bulk, while the interaction between TiO₂ and rGO creates a channel for fast transfer of excited electrons towards the latter before being recombined on the surface defect sites.

Synergetic adsorption and photocatalytic degradation of pollutants over 3D TiO2–graphene aerogel composites synthesized via a facile one-pot route

A series of 3D TiO₂–GA composites were successfully self-assembled, which exhibited excellent adsorption capacities and visible light photocatalytic activity in the degradation of RhB.

A novel & effective visible light-driven TiO2/magnetic porous graphene oxide nanocomposite for the degradation of dye pollutants

A novel & effective visible light-driven TiO₂/magnetic porous graphene oxide nanocomposite synthesized and the nanocatalyst was applied for degrading dye pollutant.