One-Pot Synthesis of TiO2-rGO Photocatalysts for the Degradation of Groundwater Pollutants

Photocatalytic Degradation of Methylene Blue and Anticancer Response of In2O3/RGO Nanocomposites Prepared by a Microwave-Assisted Hydrothermal Synthesis Process

The incorporation of graphene with metal oxide has been widely explored in various fields, including energy storage devices, optical applications, biomedical applications, and water remediation. This research aimed to assess the impact of reduced graphene oxide (RGO) doping on the photocatalytic and anticancer properties of In₂O₃ nanoparticles. Pure and In₂O₃/RGO nanocomposites were effectively synthesized using the single-step microwave hydrothermal process. XRD, TEM, SEM, EDX, XPS, Raman, UV-Vis, and PL spectroscopy were carefully utilized to characterize the prepared samples. XRD data showed that synthesized In₂O₃ nanoparticles had high crystallinity with a decreased crystal size after RGO doping. TEM and SEM images revealed that the In₂O₃ NPs were spherical and uniformly embedded onto the surface of RGO sheets. Elemental analysis of In₂O₃/RGO NC confirmed the presence of In, O, and C without impurities. Raman analysis indicated the successful fabrication of In₂O₃ onto the RGO surface. Uv-Vis analysis showed that the band gap energy was changed with RGO addition. Raman spectra confirmed that In₂O₃ nanoparticles were successfully anchored onto the RGO sheet. PL results indicated that the prepared In₂O₃/RGO NCs can be applied to enhance photocatalytic activity and biomedical applications. In the degradation experiment, In₂O₃/RGO NCs exhibited superior photocatalytic activity compared to that of pure In₂O₃. The degradation efficiency of In₂O₃/RGO NCs for MB dye was up to 90%. Biological data revealed that the cytotoxicity effect of In₂O₃/RGO NCs was higher than In₂O₃ NPs in human colorectal (HCT116) and liver (HepG2) cancer cells. Importantly, the In₂O₃/RGO NCs exhibited better biocompatibility against human normal peripheral blood mononuclear cells (PBMCs). All the results suggest that RGO addition improves the photocatalytic and anticancer activity of In₂O₃ NPs. This study highlights the potential of In₂O₃/RGO NCs as an efficient photocatalyst and therapeutic material for water remediation and biomedicine.

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.

CeO2-rGO Composites for Photocatalytic H2 Evolution by Glycerol Photoreforming

The interaction between CeO₂-GO or CeO₂-rGO and gold as co-catalysts were here investigated for solar H₂ production by photoreforming of glycerol. The materials were prepared by a solar photoreduction/deposition method, where in addition to the activation of CeO₂ the excited electrons were able to reduce the gold precursor to metallic gold and the GO into rGO. The presence of gold was fundamental to boost the H₂ production, whereas the GO or the rGO extended the visible-light activity of cerium oxide (as confirmed by UV-DRS). Furthermore, the strong interaction between CeO₂ and Au (verified by XPS and TEM) led to good stability of the CeO₂-rGO-Au sample with the evolved H₂ that increased during five consecutive runs of glycerol photoreforming. This catalytic behaviour was ascribed to the progressive reduction of GO into rGO, as shown by Raman measurements of the photocatalytic runs. The good charge carrier separation obtained with the CeO₂-rGO-Au system allowed the simultaneous production of H₂ and reduction of GO in the course of the photoreforming reaction. These peculiar features exhibited by these unconventional photocatalysts are promising to propose new solar-light-driven photocatalysts for green hydrogen production.

Acute Toxicity of a Marine Emerging Pollutant (Promethazine Hydrochloride) on Artemia sp

Recently, there has been a worrying increase in the pollution of the aquatic ecosystem caused by emerging contaminants (ECs) detected in wastewater effluent discharges. Although traces of ECs in waters have been found in low concentrations, it leads to negative effects for nontarget organisms. Antihistamines are a class of drugs largely used, whose metabolites are widespread in the aquatic ecosystem. The aim of the study was to evaluate the short-term effects of promethazine hydrochloride on nauplii of Artemia sp. A high percentage of mortality and morphological alterations were found. The results suggest a possible correlation between exposure to antihistamine and an acceleration of larval development.

Shedding light on the performance of magnetically recoverable TiO2/Fe3O4/rGO-5 photocatalyst. Degradation of S-metolachlor as case study

Recalcitrant contaminants are not usually removed in conventional wastewater treatment plants. Therefore, they are transferred to the water resources that receive treated wastewaters and their presence can cause health and environmental issues. Herbicides are among these compounds. In particular, S-metolachlor (MTLC) is specifically of high concern because its molecule incorporates a chlorine atom that contributes to its toxicity. For its removal, a magnetically recoverable photocatalyst, TiO₂/Fe₃O₄/rGO-5, was synthesised following a hydrothermal method. The performance of TiO₂/Fe₃O₄/rGO-5 has been experimentally assessed and compared to TiO₂ and TiO₂/rGO-5 catalysts. A characterisation of the materials properties was carried out including adsorption isotherms of MTLC that provided the maximum adsorption capacity of the materials (q_m), being 140.85 ± 5.14 mg g^-1 for TiO₂/Fe₃O₄/rGO-5. Furthermore, the ternary composite exhibited good recoverability from liquid media after four consecutive cycles thanks to its magnetic character (magnetic saturation of 13.85 emu g^-1). Photocatalytic degradation of MTLC started after a dark adsorption step following first order kinetics (0.0197 ± 1.2 × 10^-4 min^-1 for the degradation of 100 mg L^-1 of MTLC with 0.5 g L^-1 of TiO₂/Fe₃O₄/rGO-5) similar to the rate of appearance of chloride in solution; after total removal of the solubilized MTLC the chloride concentration in the solution continued increasing with zero-th order kinetics up to the value corresponding to the total MTLC concentration. This second step in the chloride formation was attributed to the degradation of adsorbed MTLC. Specific experiments in the presence of scavengers of reactive oxygen species (ROS) were carried out shedding light on the degradation mechanisms. It was concluded the predominant role of free hydroxyl radicals in the photocatalytic degradation in all the investigated materials, whereas the presence of rGO in the composite photocatalysts improved their electronic conductivity, enhancing the activity of superoxide radicals. The results of this work provide important information for further development of photocatalysis.

One-Pot Synthesis of SnO2-rGO Nanocomposite for Enhanced Photocatalytic and Anticancer Activity

Metal oxide and graphene derivative-based nanocomposites (NCs) are attractive to the fields of environmental remediation, optics, and cancer therapy owing to their remarkable physicochemical characteristics. There is limited information on the environmental and biomedical applications of tin oxide-reduced graphene oxide nanocomposites (SnO₂-rGO NCs). The goal of this work was to explore the photocatalytic activity and anticancer efficacy of SnO₂-rGO NCs. Pure SnO₂ NPs and SnO₂-rGO NCs were prepared using the one-pot hydrothermal method. X-ray diffraction (XRD), transmission electron microscopy (TEM), scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS), Fourier transform infrared (FTIR), UV–Vis spectrometry, photoluminescence (PL), and Raman scattering microscopy were applied to characterize the synthesized samples. The crystallite size of the SnO₂ NPs slightly increased after rGO doping. TEM and SEM images show that the SnO₂ NPs were tightly anchored onto the rGO sheets. The XPS and EDX data confirmed the chemical state and elemental composition of the SnO₂-rGO NCs. Optical data suggest that the bandgap energy of the SnO₂-rGO NCs was slightly lower than for the pure SnO₂ NPs. In comparison to pure SnO₂ NPs, the intensity of the PL spectra of the SnO₂-rGO NCs was lower, indicating the decrement of the recombination rate of the surfaces charges (e⁻/h⁺) after rGO doping. Hence, the degradation efficiency of methylene blue (MB) dye by SnO₂-rGO NCs (93%) was almost 2-fold higher than for pure SnO₂ NPs (54%). The anticancer efficacy of SnO₂-rGO NCs was also almost 1.5-fold higher against human liver cancer (HepG2) and human lung cancer (A549) cells compared to the SnO₂ NPs. This study suggests a unique method to improve the photocatalytic activity and anticancer efficacy of SnO₂ NPs by fusion with graphene derivatives.

Efficient Charge Transfer Channels in Reduced Graphene Oxide/Mesoporous TiO2 Nanotube Heterojunction Assemblies toward Optimized Photocatalytic Hydrogen Evolution

Interface engineering is usually considered to be an efficient strategy to promote the separation and migration of photoexcited electron-hole pairs and improve photocatalytic performance. Herein, reduced graphene oxide/mesoporous titanium dioxide nanotube heterojunction assemblies (rGO/TiO₂) are fabricated via a facile hydrothermal method. The rGO is anchored on the surface of TiO₂ nanosheet assembled nanotubes in a tightly manner due to the laminated effect, in which the formed heterojunction interface becomes efficient charge transfer channels to boost the photocatalytic performance. The resultant rGO/TiO₂ heterojunction assemblies extend the photoresponse to the visible light region and exhibit an excellent photocatalytic hydrogen production rate of 932.9 μmol h^-1 g^-1 under simulated sunlight (AM 1.5G), which is much higher than that of pristine TiO₂ nanotubes (768.4 μmol h^-1 g^-1). The enhancement can be ascribed to the formation of a heterojunction assembly, establishing effective charge transfer channels and favoring spatial charge separation, the introduced rGO acting as an electron acceptor and the two-dimensional mesoporous nanosheets structure supplying a large surface area and adequate surface active sites. This heterojunction assembly will have potential applications in energy fields.

Photocatalytic H2 Production on Au/TiO2: Effect of Au Photodeposition on Different TiO2 Crystalline Phases

In this work, we investigated the role of the crystalline phases of titanium dioxide in the solar photocatalytic H2 production by the reforming of glycerol, focusing the attention on the influence of photodeposited gold, as a metal co-catalyst, on TiO2 surface. We correlated the photocatalytic activity of 1 wt% Au/TiO2 in anatase, rutile, and brookite phases with the structural and optical properties determined by Raman spectroscopy, N2 adsorption–desorption measurements, UV–vis Diffuse Reflectance Spectroscopy (UV–vis DRS), X-ray photoelectron spectroscopy (XPS), Photoluminescence spectroscopy (PL), and Dynamic Light scattering (DLS). The best results (2.55 mmol H2 gcat−1 h−1) were obtained with anatase and gold photodeposited after 30 min of solar irradiation. The good performance of Au/TiO2 in anatase form and the key importance of the strong interaction between gold and the peculiar crystalline phase of TiO2 can be a starting point to efficiently improve photocatalysts design and experimental conditions, in order to favor a green hydrogen production through solar photocatalysis.