Facile synthesis of TiO2-RGO composite with enhanced performance for the photocatalytic mineralization of organic pollutants

Efficient photocatalytic bactericidal performance of green-synthesised TiO2/reduced graphene oxide using banana peel extracts

In this study, the fabrication of titanium dioxide/reduced graphene oxide (TiO2/rGO) utilising banana peel extracts (Musa paradisiaca L.) as a reducing agent for the photoinactivation of Escherichia coli (E. coli) and Staphylococcus aureus (S. aureus) was explored. The GO synthesis was conducted using a modified Tour method, whereas the production of rGO involved banana peel extracts through a reflux method. The integration of TiO2 into rGO was achieved via a hydrothermal process. The successful synthesis of TiO2/rGO was verified through various analytical techniques, including X-ray diffraction (XRD), gas sorption analysis (GSA), Fourier-transform infrared (FT-IR) spectroscopy, ultraviolet-visible diffuse reflectance spectroscopy (UV-Vis DRS), scanning electron microscope-energy dispersive X-ray (SEM-EDX) and transmission electron microscopy (TEM) analyses. The results indicated that the hydrothermal-assisted green synthesis effectively produced TiO2/rGO with a particle size of 60.5 nm. Compared with pure TiO2, TiO2/rGO demonstrated a reduced crystallite size (88.505 nm) and an enhanced surface area (22.664 m2/g). Moreover, TiO2/rGO featured a low direct bandgap energy (3.052 eV), leading to elevated electrical conductivity and superior photoconductivity. To evaluate the biological efficacy of TiO2/rGO, photoinactivation experiments targeting E. coli and S. aureus were conducted using the disc method. Sunlight irradiation emerged as the most effective catalyst, achieving optimal inactivation results within 6 and 4 h.

Efficient degradation of phenol by MnOOH-rGO composite with high peroxymonosulfate utilization efficiency

A high-performance, durable, low-cost, and environmentally friendly catalyst is highly desired in advanced oxidation processes (AOPs) for water treatment. Considering the activity of Mn(Ⅲ) and the superior catalytic properties of reduced graphene oxide (rGO) in peroxymonosulfate (PMS) activation, rGO-modified MnOOH nanowires (MnOOH-rGO) were fabricated by a hydrothermal method for phenol degradation. The results showed that the composite synthesized at 120 °C with 1 wt% rGO dopant exhibited the best performance for phenol degradation. Nearly 100% of the phenol was removed by MnOOH-rGO within 30 min, which is higher than the removal rate of pure MnOOH (70%). The effects of catalyst dosages, PMS concentration, pH, temperature, and anions (Cl-, NO3-, HPO42-and HCO3-) on phenol degradation were investigated. The removal rate of chemical oxygen demand (COD) reached 26.4%, with a low molar ratio of PMS to phenol at 5:1 and a high PMS utilization efficiency (PUE) of 88.8%. The phenol removal rate remained more than 90% after five recycle with less than 0.1 mg L-1 leakage of manganese ions. Together with the results of radical quenching experiments, X-ray photoelectron spectroscopy (XPS) and electron paramagnetic resonance spectroscopy (EPR), electron transfer and 1O2 were proved to dominate the activation process. During the direct electrons transfer process, the electrons transfer from the phenol to PMS by using the Mn(Ⅲ) as the mediate with a stoichiometric ratio between PMS and phenol at 1:2, which mainly contributed to the high PUE. This work provides new insight into a high-performance Mn(Ⅲ) based catalyst on PMS activation with high PUE, good reusability, and environmentally friendly for removing organic pollutants.

Evaluation of reduced graphene oxide-based nanomaterial as dispersive solid phase extraction sorbent for isolation and purification of aflatoxins from poultry feed, combined with UHPLC-MS/MS analysis

Poultry feed comprises cereals and their by-products and is vulnerable to aflatoxins contamination. This study utilised reduced graphene oxide-titanium dioxide (rGO-TiO2) nanomaterial as a dispersive solid phase extraction (d-SPE) adsorbent to extract, enrich and purify aflatoxins (aflatoxin B1, aflatoxin B2, aflatoxin G1 and aflatoxin G2). The synthesis of rGO-TiO2 nanomaterials through hydrothermal process and characterisation by transmission electron microscopy, scanning electron microscopy, Brunauer-Emmett-Teller (BET) and X-ray diffraction reveals that the nanomaterials have a single-layer structure embedded with TiO2 nanoparticles. The matrix-spiked technique was employed for the extraction process, optimisation of d-SPE, and analytical method validation. The most appropriate extraction solvent was acetonitrile/water/formic acid (79/20/1, v/v/v), with 30 min of extraction time assisted by ultra-sonication. The optimised d-SPE parameters were: 50 mg of rGO-TiO2 as sorbent amount, 2% methanol as the sample loading solvent, 30 min as adsorption time, and absolute ethanol as the washing reagent. The d-SPE method exhibited good desorption efficiency with 3 mL of acetonitrile/formic acid (99/1, v/v) and 20 min desorption time. After validation, the UHPLC-MS/MS analytical method has an acceptable range of specificity, linearity (R2 ≥ 0.999), sensitivity (LOQ 0.04-0.1 µg kg-1), recoveries (74-105% at three matrix-spiked levels) and precision (RSD 1.5-9.6%). Poultry feed samples (n = 12) were pretreated by this method to extract, enrich and analyse aflatoxins, which were detected in all poultry feed samples. The contamination levels were within the permissible limits.

Titania/reduced graphene oxide nanocomposites (TiO2/rGO) as an efficient photocatalyst for the effective degradation of brilliant green in aqueous media: effect of peroxymonosulfate and operational parameters

This study is focused on synthesis of highly efficient Titania/reduced Graphene Oxide (TiO₂/rGO) nanocomposites by means of simple hydrothermal technique. The TiO₂/rGO were synthesized in different ratios of 0.5, 1.0, 2.0, and 3% by varying the concentration of rGO while the concentration of TiO₂ was kept constant and the obtained samples were designated as TrG0.5, TrG1, TrG2, and TrG3 respectively. Different characterization techniques (SEM, TEM, HRTEM, XRD, EDX, TGA, UV-DRS, PL, EIS, and BET) showed high crystallinity, small crystallite size (18.4 nm), high thermal stability, high purity, low band gap energy (E_g = 3.12 eV), and high surface area (65.989 m²/g) for the as-synthesized TiO₂/rGO nanocomposite. The efficiencies of TiO₂/rGO were determined in terms of brilliant green (BG) dye degradation in aqueous media under UV light. The results revealed that 2% TiO₂/rGO (TrG2) showed high efficiency for BG degradation with the k_app of 0.023 min^-1 compared to TiO₂ alone (k_app of 0.006 min^-1). The rate of BG degradation was further synergised by the addition of peroxymonosulfate (PMS) to the system. The degradation of BG was improved to 99.4% by the incorporation of PMS in aqueous media compared to TrG2 alone. Furthermore, the degradation of BG was also examined in various media (neutral, acidic, and basic). The results revealed that by increasing pH of the medium from 3.85 to 8.2 the degradation of BG was enhanced from 99.4 to 99.9% with the corresponding k_app of 0.0602 min^-1. Moreover, the photocatalytic degradation of BG followed the pseudo-first-order kinetics. Radical scavenging experiments showed that ^●OH and SO₄^●- were the main species responsible for the degradation of BG under UV light. Besides, for determining the efficiency of as-synthesized TrG2/PMS system, the degradation of BG was also performed in various water types (distilled water, tape water, synthetic wastewater, and industrial wastewater). The degradation products (DPs) of BG and their corresponding pathways were proposed, accordingly.

Solar light-driven photocatalytic degradation and mineralization of beta blockers propranolol and atenolol by carbon dot/TiO2 composite

Herein improved solar light-driven photocatalytic degradation and mineralization of two emerging pollutants as well as recalcitrant beta blockers propranolol (PR) and atenolol (AT) have been demonstrated by metal-free carbon dot/TiO₂ (CDT) composite. Hydrothermally synthesized TiO₂ has been decorated with electrochemically synthesized carbon dots (CDs) and was well characterized by various analytical techniques viz. XRD, FTIR, Raman, XPS, UV-visible DRS, FESEM, and TEM. The optimized CDT composite, 2CDT (2 mL carbon dot/TiO₂), showed ~ 3.45- and ~ 1.75-fold enhancement in the photodegradation rate as compared to pristine TiO₂ for PR and AT respectively in 1 hour of irradiation along with complete degradation of PR and AT after 3 hours of irradiation. 2CDT exhibited 76% and 80% mineralization of PR and AT in contrast with 62% and 47% observed by pristine TiO₂. Further, the major reaction intermediates formed after degradation have been identified by HPLC/MS analysis, confirming more than 99% reduction of the parent compound for both PR and AT. Reusability of the optimized catalyst also showed successful degradation up to 3 cycles, showing reduction abilities of 97%, 95%, and 94% for 1st, 2nd, and 3rd cycle respectively. The enhanced degradation and mineralization efficiency of the 2CDT composite could be attributed to the excellent photosensitizer and electron reservoir properties of the CD along with upconverted photoluminescence behavior. The present study unlocks the possibility of using metal-free, facile CDT composite for effective degradation and mineralization of widely used beta blockers and other pharmaceuticals.

Preparation of Ag3PO4/α-Fe2O3 hybrid powders and their visible light catalytic performances

The inefficiency of conventional photocatalytic treatment for removing rhodamine B is posing potential risks to ecological environments. Here, we construct a highly efficient photocatalyst consisting of Ag₃PO₄ and α-Fe₂O₃ hybrid powders for the treatment of rhodamine B. Ag₃PO₄ nanoparticles (nanoparticles, about 50 nm) are uniformly dispersed on the surface of α-Fe₂O₃ microcrystals (hexagonal sheet, about 1.5 μm). The Ag₃PO₄-deposited uniformity on the α-Fe₂O₃ surface first increased, then decreased on increasing the hybrid ratio of Ag₃PO₄ to α-Fe₂O₃. When the hybrid ratio of Ag₃PO₄ to α-Fe₂O₃ is 1 : 2, the distribution of Ag₃PO₄ particles on the sheet α-Fe₂O₃ is more uniform with excellent Ag₃PO₄/α-Fe₂O₃ interface performance. The catalytic degradation efficiency of hybrids with the introduction of Ag₃PO₄ nanoparticles on the α-Fe₂O₃ surface reached 95%. More importantly, the hybrid material exhibits superior photocatalytic stability. Ag₃PO₄/α-Fe₂O₃ hybrids have good reusability, and the photocatalytic efficiency could still reach 72% after four reuses. The excellent photocatalytic activity of the as-prepared hybrids can be attributed to the heterostructure between Ag₃PO₄ and α-Fe₂O_3, which can effectively inhibit the photoelectron-hole recombination and broaden the visible light response range.

Facile and Green Fabrication of Microwave-Assisted Reduced Graphene Oxide/Titanium Dioxide Nanocomposites as Photocatalysts for Rhodamine 6G Degradation

Organic pollutants, such as synthetic dyes, are treated to prevent them from contaminating natural water sources. One of the treatment methods is advanced oxidation process using a photocatalyst material as the active agent. However, many photocatalysts are hindered by their production cost and efficiency. In this study, nanocomposites consisting of reduced graphene oxide and titanium dioxide (rGO/TiO2) were prepared by a simple and green approach using the microwave-assisted method, and we utilized a graphene oxide (GO) precursor that was fabricated through the Tour method. The ratios of rGO/TiO2 in nanocomposites were varied (2:1, 1:1, and 1:2) to know the influence of rGO on the photocatalytic performance of the nanocomposites for rhodamine 6G degradation. Transmission electron microscopy (TEM) observation revealed that a transparent particle with a sheetlike morphology was detected in the rGO sample, suggesting that a very thin film of a few layers of GO or rGO was successfully formed. Based on scanning electron microscopy (SEM) observation, the rGO/TiO2 nanocomposites had a wrinkled and layered rGO structure decorated by TiO2 nanoparticles with average diameters of 125.9 ± 40.6 nm, implying that rGO layers are able to prevent TiO2 from agglomeration. The synthesized product contained only rGO and TiO2 in the anatase form without impurities that were proven by Raman spectra and X-ray diffraction (XRD). The nanocomposite with rGO/TiO2 ratio 1:2 (composite C) was found to be the best composition in this study, and it was able to degrade 82.9 ± 2.4% of the rhodamine 6G after UV irradiation for 4 h. Based on a time-resolved photoluminescence study at wavelength emission 500 nm, the average decay lifetime of R6G-rGO/TiO2 composites (2.91 ns) was found to be longer than that of the R6G-TiO2 sample (2.05 ns), implying that the presence of rGO in rGO/TiO2 composites successfully suppressed the electron-hole recombination process in TiO2 and significantly improved their photocatalytic performance. This study showed that the rGO/TiO2 nanocomposites synthesized through relatively simple and eco-friendly processes display promising prospects for photocatalytic degradation of dyes and other recalcitrant pollutants in a water stream.

RSM-Based Preparation and Photoelectrocatalytic Performance Study of RGO/TiO2 NTs Photoelectrode

In this paper, reduced graphene oxide (RGO) was prepared by a modified Hummers method and chemical reduction method, and an RGO/TiO2 NTs (RGO/TiO2 nanotubes) photoelectrode was prepared by the electrochemical deposition method. The as-prepared RGO/TiO2 NTs were analyzed by scanning electron microscopy (SEM) and X-ray diffraction (XRD), and their photocatalytic activities were investigated by measuring the degradation of methylene blue (MB) under simulated solar light irradiation. The SEM and XRD results indicated that the original tubular structure of TiO2-NTs was not changed after RGO modification. The surface of the TiO2 NTs photoelectrode was covered with a non-uniform, flake-shaped reduced graphene oxide film. The thickness of the RGO/TiO2 NTs was increased to about 22.60 nm. The impedance of the RGO/TiO2 NTs was smaller than that of the TiO2 NT photoelectrode. The optimal preparation conditions of RGO/TiO2 NT photoelectrodes were investigated by using a single factor method and response surface method. The best preparation conditions were as follows: deposition potential at 1.19 V, deposition time of 10.27 min, and deposition temperature at 24.94 °C.

Development and Characterization of Composite Carbon Adsorbents with Photocatalytic Regeneration Ability: Application to Diclofenac Removal from Water

This paper presents results related to the development of a carbon composite intended for water purification. The aim was to develop an adsorbent that could be regenerated using light leading to complete degradation of pollutants and avoiding the secondary pollution caused by regeneration. The composites were prepared by hydrothermal carbonization of palm kernel shells, TiO2, and W followed by activation at 400 °C under N2 flow. To evaluate the regeneration using light, photocatalytic experiments were carried out under UV-A, UV-B, and visible lights. The materials were thoroughly characterized, and their performance was evaluated for diclofenac removal. A maximum of 74% removal was observed with the composite containing TiO2, carbon, and W (HCP25W) under UV-B irradiation and non-adjusted pH (~5). Almost similar results were observed for the material that did not contain tungsten. The best results using visible light were achieved with HCP25W providing 24% removal of diclofenac, demonstrating the effect of W in the composite. Both the composites had significant amounts of oxygen-containing functional groups. The specific surface area of HCP25W was about 3 m2g−1, while for HCP25, it was 160 m2g−1. Increasing the specific surface area using a higher activation temperature (600 °C) adversely affected diclofenac removal due to the loss of the surface functional groups. Regeneration of the composite under UV-B light led to a complete recovery of the adsorption capacity. These results show that TiO2- and W-containing carbon composites are interesting materials for water treatment and they could be regenerated using photocatalysis.

One-Pot Synthesis of Sulfur-Doped TiO2/Reduced Graphene Oxide Composite (S-TiO2/rGO) With Improved Photocatalytic Activity for the Removal of Diclofenac From Water

Sulfur-doped TiO2 (S-TiO2) composites with reduced graphene oxide (rGO), wt. % of rGO equal to 0.5%, 2.75%, and 5.0%, were prepared by a one-pot solvothermal procedure. The aim was to improve photocatalytic performance in comparison to TiO2 under simulated solar irradiation for the treatment of diclofenac (DCF) in aqueous medium. The obtained composites were characterized for physical-chemical properties using thermogravimetric analysis (TGA), X-ray diffractograms (XRD), Raman, scanning electron microscopy (SEM)/energy dispersive X-ray (EDX), Brauner Emmett Teller (BET), and photoluminescence (PL) analyses, indicating successful sulfur doping and inclusion of rGO. Sulfur doping and rGO have successfully led to a decrease in photogenerated charge recombination. However, both antagonistic and synergistic effects toward DCF treatment were observed, with the latter being brought forward by higher wt.% rGO. The composite with 5.0 wt.% rGO has shown the highest DCF conversion at pH 4 compared to that obtained by pristine TiO2, despite lower DCF adsorption during the initial dark period. The expected positive effects of both sulfur doping and rGO on charge recombination were found to be limited because of the subpar interphase contact with the composite and incomplete reduction of the GO precursor. Consequent unfavorable interactions between rGO and DCF negatively influenced the activity of the studied S-TiO2/rGO photocatalyst under simulated solar irradiation.

Photocatalytic degradation and mineralization of perfluorooctanoic acid (PFOA) using a composite TiO2 -rGO catalyst

The inherent resistance of perfluoroalkyl substances (PFASs) to biological degradation makes necessary to develop advanced technologies for the abatement of this group of hazardous substances. The present work investigated the photocatalytic decomposition of perfluorooctanoic acid (PFOA) using a composite catalyst based on TiO₂ and reduced graphene oxide (95% TiO₂/5% rGO) that was synthesized using a facile hydrothermal method. The efficient photoactivity of the TiO₂-rGO (0.1gL^-1) composite was confirmed for PFOA (0.24mmolL^-1) degradation that reached 93±7% after 12h of UV-vis irradiation using a medium pressure mercury lamp, a great improvement compared to the TiO₂ photocatalysis (24±11% PFOA removal) and direct photolysis (58±9%). These findings indicate that rGO provided the suited properties of TiO₂-rGO, possibly as a result of acting as electron acceptor and avoiding the high recombination electron/hole pairs. The release of fluoride and the formation of shorter-chain perfluorocarboxilyc acids, that were progressively eliminated in a good match with the analysed reduction of total organic carbon, is consistent with a step-by-step PFOA decomposition via photogenerated hydroxyl radicals. Finally, the apparent first order rate constants of the TiO₂-rGO UV-vis PFOA decompositions, and the intermediate perfluorcarboxylic acids were found to increase as the length of the carbon chain was shorter.

Ultrasonic spray pyrolysis synthesis of reduced graphene oxide/anatase TiO2 composite and its application in the photocatalytic degradation of methylene blue in water

Reduced graphene oxide (RGO)/anatase TiO₂ composite was prepared using a simple one-step technique-ultrasonic spray pyrolysis-in order to inhibit the aggregation of TiO₂ nanoparticles and to improve the photocatalytic performance for degradation of methylene blue (MB). Different proportions (0-5 wt%) of RGO/TiO₂ composites were characterized by scanning electronic microscopy (SEM), dispersive X-ray spectrometry (EDS), transmission electron microscopy (TEM), Brunauer-Emmett-Teller (BET) surface area, X-ray photoelectron spectroscopy (XPS), X-ray diffractometry (XRD), Raman spectroscopy, UV-vis spectroscopy, and electrochemical impedance spectroscopy (EIS) to verify mechanism. From these analysis, TiO₂ nanoparticles are distributed uniformly on the RGO sheets with crumpled shape during ultrasonic spray pyrolysis and surface area is increasing by increasing portion of RGO. Band gap of RGO₅/TiO₂ (5 wt% of RGO) composite is 2.72 eV and band gap was reduced by increasing portion of RGO in RGO/TiO₂ composites. The RGO₅/TiO₂ composite was superior to other lower content of RGO/TiO₂ composites with a rapid transport of charge carriers and an effective charge separation. The highest removal efficiency of MB was obtained at the RGO₅/TiO₂ composite under UVC irradiation, which coincided with the EIS, and the optimal dose of the composite was determined to be 0.5 g/L. The RGO₅/TiO₂ composite improve the photocatalytic degradation rate of MB over the TiO₂ due to a retardation of electron-hole recombination. The MB adsorption capacity and photocatalytic degradation efficiency were greatly affected by pH changes and increased with increasing pH due to electrostatic interactions and generation of more hydroxyl radicals. The reusability of RGO₅/TiO₂ composite was examined during 3 cycles.

Non-light-driven reduced graphene oxide anchored TiO2 nanocatalysts with enhanced catalytic oxidation performance

As a single-atom-thick carbon material with high surface and good conductivity, graphene provides an ideal platform for designing composite nanomaterials for high-performance catalytic system. Herein, we obtained a TiO₂-reduced graphene oxide nanocomposite (TiO₂-RGO) with graphene oxide and tetrabutyl titanate using a facile in situ hydrothermal method. The merit of this method is that the nanocomposites could be produced directly from graphene oxide in the hydrothermal reaction, where the reduction of graphene oxide and the decoration of TiO₂ occurred simultaneously. TiO₂ nanoparticles anchored on graphene sheets as spacers to keep the neighboring sheets separated. The in situ growth route provides a desirable platform for constructing graphene-supported nanocomposites with improved properties. As one of the major applications of the nanocomposites, we investigate the performance of as-prepared TiO₂-RGO as effective non-light-driven catalysts for activating H₂O₂ in oxidative degradation of the dye. The system was employed in oxidation degradation not only to reach high degradation efficiency but also to avoid any energy consumption. Meanwhile, the proposed catalytic system processes broad-spectrum oxidative degradation activity for different model organic pollutants. Overall, this work could provide new insights into the fabrication of a TiO₂-RGO as high performance catalysts and facilitate their application in the environmental protection issues.

Synthesis and photocatalytic performance of reduced graphene oxide-TiO2 nanocomposites for orange II degradation under UV light irradiation

To enhance the photocatalytic activity of TiO₂, reduced graphene oxide-TiO₂ (RGO-TiO₂) composites with sandwich-like structure were synthesized using a simple solvothermal method. The morphology, crystalline information, and structural property of the photocatalyst were characterized by field emission scanning electron microscopy, transmission electron microscopy, X-ray diffraction, and Fourier transmission infrared spectroscopy. The photocatalytic performances of the RGO-TiO₂ composites were evaluated by the degradation of orange II (AO7) in water under UV light irradiation. The results showed that the RGO-TiO₂ composites exhibited much higher photocatalytic activity than TiO₂ and that the removal efficiency of AO7 could reach above 95% only after 20 min of UV light irradiation under the optimum condition. The improved photocatalytic activity might be attributed to the improved charge transfer and significant separation of the photoinduced electrons and holes in the presence of a two-dimensional graphene network. The results of recycling experiments show that RGO-TiO₂ composites have a high photostability, which is expected in the practical application. Radical trapping experiments indicated that ·OH plays a crucial role in the process of AO7 degradation.

Nanostructured BN–TiO2 composite with ultra-high photocatalytic activity

Boron nitride and titanium oxide composite (BN–TiO₂) photocatalyst endowed with high specific surface area and large pore size was synthesized by ice bath method.

Enhanced photocatalytic performance of novel electrospun BN/TiO2 composite nanofibers

We report the elaboration of novel BN/TiO₂ composite nanofibers with different amounts of BN sheets and their photocatalytic activity under UV irradiation.