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

Heterogeneous electro-Fenton treatment of chemotherapeutic drug busulfan using magnetic nanocomposites as catalyst

The rapid and efficient mineralization of the chemotherapeutic drug busulfan (BSF) as the target pollutant has been investigated for the first time by three different heterogeneous EF systems that were constructed to ensure the continuous electro-generation of H2O2 and •OH consisting of: i) a multifunctional carbon felt (CF) based cathode composed of reduced graphene oxide (rGO), iron oxide nanoparticles and carbon black (CB) (rGO-Fe3O4/CB@CF), ii) rGO modified cathode (rGO/CB@CF) and rGO supported Fe3O4 (rGO-Fe3O4) catalyst and iii) rGO modified cathode (rGO/CB@CF) and multi walled carbon nanotube supported Fe3O4 (MWCNT-Fe3O4) catalyst. The effects of main variables, including the catalyst amount, applied current and initial pH were investigated. Based on the results, H2O2 was produced by oxygen reduction reaction (ORR) on the liquid-solid interface of both fabricated cathodes. •OH was generated by the reaction of H2O2 with the active site of ≡FeII on the surface of the multifunctional cathode and heterogeneous EF catalysts. Utilizing carbon materials with high conductivity, the redox cycling between ≡FeII and ≡FeIII was effectively facilitated and therefore promoted the performance of the process. The results demonstrated almost complete mineralization of BSF through the heterogeneous systems over a wide applicable pH range. According to the reusability and stability tests, multifunctional cathode exhibited outstanding performance after five consecutive cycles which is promising for the efficient mineralization of refractory organic pollutants. Moreover, intermediates products of BSF oxidation were identified and a plausible oxidation pathway was proposed. Therefore, this study demonstrates efficient and stable cathodes and catalysts for the efficient treatment of an anticancer active substance.

Synergistic Remediation of Organic Dye by Titanium Dioxide/Reduced Graphene Oxide Nanocomposite

In this work, nanocomposites based on titanium dioxide and reduced graphene oxide (TiO2@rGO) with different weight percentages of rGO (4, 8, and 16 wt%) were prepared by the hydrothermal/solvothermal synthesis method and thermally treated at 300 °C. The prepared nanocomposites were explored for the removal of methylene blue dye (MB) in the presence of simulated solar illumination as well as natural sunlight. The structural, morphological, chemical, and optical properties of the as-synthesized TiO2@rGO nanocomposites were characterized. The obtained results of the graphene-based nanocomposite materials indicated the existence of interactions between TiO2 and rGO, i.e., the Ti-O-C bond, which confirmed the successful integration of both components to form the TiO2@rGO nanocomposites. The addition of rGO increased the specific surface area, decreased the band gap energy, and increased the photocatalytic degradation efficiency of MB from water compared to TiO2 nanoparticles. The results of photocatalytic activity indicated that the amount of rGO in the prepared TiO2@rGO nanocomposites played a significant role in the application of different photocatalytic parameters, including the initial dye concentration, catalyst concentration, water environment, and illumination source. Our studies show that the reinforcement of the nanocomposite with 8 wt% of rGO allowed us to obtain the maximum photocatalytic decomposition performance of MB (10 mg·L-1) with a removal percentage of 99.20 after 2 h. Additionally, the obtained results show that the prepared TiO2@rGO_8 wt% nanocomposite can be used in three consecutive cycles while maintaining photocatalytic activity over 90%.

Hydrothermal Synthesis of Heterostructured g-C3N4/Ag-TiO2 Nanocomposites for Enhanced Photocatalytic Degradation of Organic Pollutants

In this study, heterostructured g-C3N4/Ag-TiO2 nanocomposites were successfully fabricated using an easily accessible hydrothermal route. Various analytical tools were employed to investigate the surface morphology, crystal structure, specific surface area, and optical properties of as-synthesized samples. XRD and TEM characterization results provided evidence of the successful fabrication of the ternary g-C3N4/Ag-TiO2 heterostructured nanocomposite. The heterostructured g-C3N4/Ag-TiO2 nanocomposite exhibited the best degradation efficiency of 98.04% against rhodamine B (RhB) within 180 min under visible LED light irradiation. The g-C3N4/Ag-TiO2 nanocomposite exhibited an apparent reaction rate constant 13.16, 4.7, and 1.33 times higher than that of TiO2, Ag-TiO2, and g-C3N4, respectively. The g-C3N4/Ag-TiO2 ternary composite demonstrated higher photocatalytic activity than pristine TiO2 and binary Ag-TiO2 photocatalysts for the degradation of RhB under visible LED light irradiation. The improved photocatalytic performance of the g-C3N4/Ag-TiO2 nanocomposite can be attributed to the formation of an excellent heterostructure between TiO2 and g-C3N4 as well as the incorporation of Ag nanoparticles, which promoted efficient charge carrier separation and transfer and suppressed the rate of recombination. Therefore, this study presents the development of heterostructured g-C3N4/Ag-TiO2 nanocomposites that exhibit excellent photocatalytic performance for the efficient degradation of harmful organic pollutants in wastewater, making them promising candidates for environmental remediation.

Single-Step Synthesis of Graphitic Carbon Nitride Nanomaterials by Directly Calcining the Mixture of Urea and Thiourea: Application for Rhodamine B (RhB) Dye Degradation

Recently, polymeric graphitic carbon nitride (g-C₃N₄) has been explored as a potential catalytic material for the removal of organic pollutants in wastewater. In this work, graphitic carbon nitride (g-C₃N₄) photocatalysts were synthesized using mixtures of low-cost, environment-friendly urea and thiourea as precursors by varying calcination temperatures ranging from 500 to 650 °C for 3 h in an air medium. Different analytical methods were used to characterize prepared g-C₃N₄ samples. The effects of different calcination temperatures on the structural, morphological, optical, and physiochemical properties of g-C₃N₄ photocatalysts were investigated. The results showed that rhodamine B (RhB) dye removal efficiency of g-C₃N₄ prepared at a calcination temperature of 600 °C exhibited 94.83% within 180 min visible LED light irradiation. Photocatalytic activity of g-C₃N₄ was enhanced by calcination at higher temperatures, possibly by increasing crystallinity that ameliorated the separation of photoinduced charge carriers. Thus, controlling the type of precursors and calcination temperatures has a great impact on the photocatalytic performance of g-C₃N₄ towards the photodegradation of RhB dye. This investigation provides useful information about the synthesis of novel polymeric g-C₃N₄ photocatalysts using a mixture of two different environmentally benign precursors at high calcination temperatures for the photodegradation of organic pollutants.

Fabrication of Novel Heterostructure-Functionalized Graphene-Based TiO2-Sr-Hexaferrite Photocatalyst for Environmental Remediation

Novel visible-light photocatalyst (titanium-dioxide-functionalized graphene/strontium-hexaferrites) TiO₂-FG/Sr-hexaferrite nanocomposites were fabricated using a simple hydrothermal technique. X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM), diffuse reflectance spectroscopy (DRS), transmission electron microscopy (TEM), Raman spectroscopic analysis, and atomic force microscopy were used to analyze the composites as prepared. The unique TiO₂-FG/Sr-hexaferrite-based composite catalyst reveals superior photocatalytic properties for the disintegration of organic dyes methylene blue (MB) and rhodamine B (Rh. B) under visible-light irradiation. The result showed that the functionalized graphene with ternary structure improved the catalytic behavior of the composite due to the synergistic effect of the TiO₂-FG boosted by the graphene surface to provide a fast conducting path to the photogenerated charge carrier. The markedly high photocatalytic behavior has been ascribed to the formation of the ternary structure between TiO₂, FG, and Sr-hexaferrites through interface interaction. The prepared photocatalyst composite exhibited better recyclability, which further confirms its future uses as a photocatalyst in industrial waste products.

Synthesis and Structure of ZnO-Decorated Graphitic Carbon Nitride (g-C3N4) with Improved Photocatalytic Activity under Visible Light

The volume of dye production in the chemical industry is growing rapidly every year. Given the global importance of clean water resources, new wastewater treatment solutions are required. Utilizing photocatalysis by harvesting solar energy represents a facile and promising solution for removing dangerous pollutants. This study reports the possibility of increasing the photocatalytic activity of g-C3N4 by creating nanocomposites with ZnO. Exfoliated g-C3N4/ZnO nanocomposites were synthesized by heat treatment of urea and subsequent ultrasonic exfoliation of the colloidal solution by introducing zinc acetate. The uniformity of the distribution of ZnO nanoparticles is confirmed by the method of elemental mapping. The obtained X-ray diffractograms of the obtained nanocomposites show typical X-ray reflections for g-C3N4 and ZnO. It was found that the introduction of oxide into g-C3N4 leads to an increase in the specific surface area values due to the developed ZnO surface. The maximum value of the specific surface area was obtained for a sample containing 7.5% ZnO and was 75.2 m2/g. The g-C3N4/7.5% ZnO sample also demonstrated increased photocatalytic activity during the decomposition of methylene blue under the influence of visible light, which led to a twofold increase in the reaction rate compared to initial g-C3N4.

TiO2-Based Heterostructure Containing g-C3N4 for an Effective Photocatalytic Treatment of a Textile Dye

Water pollution has become a serious environmental issue. The textile industries using textile dyes are considered to be one of the most polluting of all industrial sectors. The application of solar-light semiconductor catalysts in wastewater treatment, among which TiO2 can be considered a prospective candidate, is limited by rapid recombination of photogenerated charge carriers. To address these limitations, TiO2 was tailored with graphitic carbon nitride (g-C3N4) to develop a heterostructure of g-C3N4@TiO2. Herein, a simple hydrothermal synthesis of TiO2@g-C3N4 is presented, using titanium isopropoxide (TTIP) and urea as precursors. The morphological and optical properties and the structure of g-C3N4, TiO2, and the prepared heterostructure TiO2@g-C3N4 (with different wt.% up to 32%), were analyzed by various laboratory methods. The photocatalytic activity was studied through the degradation of methylene blue (MB) aqueous solution under UV-A and simulated solar irradiation. The results showed that the amount of g-C3N4 and the irradiation source are the most important influences on the efficiency of MB removal by g-C3N4@TiO2. Photocatalytic degradation of MB was also examined in realistic conditions, such as natural sunlight and different aqueous environments. The synthesized g-C3N4@TiO2 nanocomposite showed superior photocatalytic properties in comparison with pure TiO2 and g-C3N4, and is thus a promising new photocatalyst for real-life implementation. The degradation mechanism was investigated using scavengers for electrons, photogenerated holes, and hydroxyl radicals to find the responsible species for MB degradation.

Rapid Microwave-Assisted Synthesis of N/TiO2/rGO Nanoparticles for the Photocatalytic Degradation of Pharmaceuticals

Nanocomposites comprising nitrogen-doped TiO₂ and reduced graphene oxide (N/TiO₂/rGO), with different rGO loading qualities, were prepared by a cost-effective microwave-assisted synthesis method. The synthesized materials were broadly characterized by Raman spectroscopy, X-ray diffraction (XRD), infrared spectroscopy (FTIR), photoelectron spectroscopy (XPS), diffuse reflectance spectroscopy (DRS), electron microscopy (SEM-EDS), and nitrogen adsorption/desorption isotherms. Anatase was the only crystalline phase observed for all synthesized materials. The rGO loading did not affect the morphological properties, but it positively influenced the photocatalytic activity of the nanocomposite materials, especially at low rGO loading. Photocatalysts were evaluated via the degradation of specific organic micropollutant (OMP) pharmaceuticals: ciprofloxacin (CIP), diclofenac (DCF), and salicylic acid (SA), under different radiation sources: ultraviolet A (UVA), solar light simulator (SLS), blue visible light (BVL) and cold visible light (CVL). CIP and SA were removed effectively via the synergy of adsorption and photocatalysis, while DCF degradation was achieved solely by photocatalysis. After implementing scavenger agents, photocatalytic degradation processes mainly depended on the specific pollutant type, while irradiation sources barely defined the photocatalytic mechanism. On the other hand, changes in irradiation intensity significantly influenced the photolysis process, while photocatalysis was slightly affected, indicating that irradiation spectra are more relevant than intensity.

GO-TiO2 as a Highly Performant Photocatalyst Maximized by Proper Parameters Selection

The synthesis and characterization of novel graphene oxide coupled to TiO₂ (GO-TiO₂) was carried out in order to better understand the performance of this photocatalyst, when compared to well-known TiO₂ (P25) from Degussa. Thus, its physical-chemical characterization (FTIR, XRD, N₂ isotherms and electrochemical measurements) describes high porosity, suitable charge and high electron mobility, which enhance pollutant degradation. In addition, the importance of the reactor set up was highlighted, testing the effect of both the irradiated area and distance between lamp and bulb solution. Under optimal conditions, the model drug methylthioninium chloride (MC) was degraded and several parameters were assessed, such as the water matrix and the catalyst reutilization, a possibility given the addition of H₂O₂. The results in terms of energy consumption compete with those attained for the treatment of this model pollutant, opening a path for further research.

Microwave-Assisted Synthesis of N/TiO2 Nanoparticles for Photocatalysis under Different Irradiation Spectra

Nitrogen-doped TiO₂ (N/TiO₂) photocatalyst nanoparticles were derived by the environmentally friendly and cost-effective microwave-assisted synthesis method. The samples were prepared at different reaction parameters (temperature and time) and precursor ratio (amount of nitrogen source; urea). The obtained materials were characterized by X-ray diffraction (XRD), photoelectron spectroscopy (XPS), Raman spectroscopy (RS), infrared spectroscopy (FTIR), diffuse reflectance spectroscopy (DRS), electron microscopy (SEM-EDS), and nitrogen adsorption/desorption isotherms. Two cycles of optimizations were conducted to determine the best reaction temperature and time, as well as N content. The phase composition for all N/TiO₂ nanomaterials was identified as photoactive anatase. The reaction temperature was found to be the most relevant parameter for the course of the structural evolution of the samples. The nitrogen content was the least relevant for the development of the particle morphology, but it was important for photocatalytic performance. The photocatalytic activity of N/TiO₂ nanoparticle aqueous suspensions was evaluated by the degradation of antibiotic ciprofloxacin (CIP) under different irradiation spectra: ultraviolet A light (UVA), simulated solar light, and visible light. As expected, all prepared samples demonstrated efficient CIP degradation. For all irradiation sources, increasing synthesis temperature and increasing nitrogen content further improved the degradation efficiencies.

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.

Oxygen-Deficient WO3/TiO2/CC Nanorod Arrays for Visible-Light Photocatalytic Degradation of Methylene Blue

At present, TiO2 is one of the most widely used photocatalytic materials. However, the narrow response range to light limits the photocatalytic performance. Herein, we reported a successful construction of self-doped R-WO3/R-TiO2/CC nanocomposites on flexible carbon cloth (CC) via electrochemical reduction to increase the oxygen vacancies (Ovs), resulting in an enhanced separation efficiency of photo-induced charge carriers. The photocurrent of R-WO3/R-TiO2/CC at −1.6 V (vs. SCE) was 2.6 times higher than that of WO3/TiO2/CC, which suggested that Ovs could improve the response to sunlight. Moreover, the photocatalytic activity of R-WO3/TiO2/CC was explored using methylene blue (MB). The degradation rate of MB could reach 68%, which was 1.3 times and 3.8 times higher than that of WO3/TiO2/CC and TiO2/CC, respectively. Furthermore, the solution resistance and charge transfer resistance of R-WO3/R-TiO2/CC were obviously decreased. Therefore, the electrochemical reduction of nanomaterials enabled a promoted separation of photogenerated electron–hole pairs, leading to high photocatalytic activity.