Hydrothermal synthesis of ZnO-graphene oxide microrod composites for photocatalytic degradation of methylene blue

The current study focuses on graphene oxide (GO) and its composite with zinc oxide and titanium dioxide nanoparticles to develop a simple nano chemistry-based clean and efficient process for the effective degradation of methylene blue (MB) dye. Graphene oxide composite with zinc oxide and titanium dioxide nanoparticles were fabricated via a thermal coupling process that demonstrates exclusive physiochemical properties. A detailed comparison of the structure, morphology, and surface analysis of synthesized GO and nanocomposites, as well as their electrochemical properties, has been accomplished. By using the degradation of methylene blue (MB) dye the photocatalytic function of nanocomposites was studied. Results reveal that the rate constants of GO, GO-TiO2, and GO-ZnO photocatalysts are 1.06 × 10−3 min−1, 2.56 × 10−3 min−1, and 1.63 × 10−3 min−1 respectively which discloses GO-TiO2 nanocomposite shows maximum degradation of MB dye among both catalysts. The reuse of photocatalyst even after five cycles retained the degradation efficiency of 80, 77, and 49% respectively for GO-TiO2, GO-ZnO, and GO when tested against MB. Hence, as a result, it was determined that these photocatalysts are ideal for the remediation of dye-contaminated wastewater.

Nanopillars-TiO2 thin films was obtained on a borosilicate glass substrate with (S1) and without (S2) polyethylene glycol as template. The photocatalytic behaviour of S1 and S2 thin films was assessed inthe degradation of methylene blue (MB) dye from aqueous solution under batch reactor operations. The thin films were characterized by the SEM, XRD, FTIR and AFM analytical methods. BET specific surface area and pore sizes were also obtained. The XRD data confirmed that the TiO2 particles are in its anatase mineral phase. The SEM and AFM images indicated the catalyst is composed with nanosized pillars of TiO2, evenly distributed on the surface of the substrate. The BET specific surface area and pore sizes of S1 and S2 catalyst were found to be 5.217 and 1.420 m2/g and 7.77 and 4.16 nm respectively. The photocatalytic degradation of MB was well studied at wide range of physico-chemical parameters. The effect of solution pH (pH 4.0 to 10.0) and MB initial concentration (1.0 to 10.0 mg/L) was extensively studied and the effect of several interfering ions, i.e., cadmium nitrate, copper sulfate, zinc chloride, sodium chloride, sodium nitrate, sodium nitrite, glycine, oxalic acid and EDTA in the photocatalytic degradation of MB was demonstrated. The maximum percent removal of MB was observed at pH 8.0 beyond which it started decreasing and a low initial concentration of the pollutant highly favoured the photocatalytic degradation using thin films and the presence of several interfering ions diminished the photocatalytic activity of thin films to some extent. The overall photocatalytic activity was in the order: S2 > S1 > UV. The photocatalytic degradation of MB was followed the pseudo-first-order rate kinetics. The mineralization of MB was studied with total organic carbon measurement using the TOC (total organic carbon) analysis.

Methylene blue (MB) is a toxic contaminant present in wastewater. Here, we prepared various composites of graphene oxide (GO) with graphitic carbon nitride (g-C3N4) and zinc oxide (ZnO) for the degradation of MB. In comparison to ZnO (22.9%) and g-C3N4/ZnO (76.0%), the ternary composites of GO/g-C3N4/ZnO showed 90% photocatalytic degradation of MB under a light source after 60 min. The experimental setup and parameters were varied to examine the process and effectiveness of MB degradation. Based on the results of the experiments, a proposed photocatalytic degradation process that explains the roles of GO, ZnO, and g-C3N4 in improving the photocatalytic efficacy of newly prepared GO/g-C3N4/ZnO was explored. Notably, the g-C3N4/ZnO nanocomposite's surface was uniformly covered with ZnO nanorods. The images of the samples clearly demonstrated the porous nature of GO/g-C3N4/ZnO photocatalysts, and even after being mixed with GO, the g-C3N4/ZnO composite retained the layered structure of the original material. The catalyst's porous structure plausibly enhanced the degradation of the contaminants. The high-clarity production of g-C3N4 and the effectiveness of the synthesis protocol were later validated by the absence of any trace contamination in the energy-dispersive X-ray spectroscopy (EDS) results. The composition of the ZnO elements and their spectra were revealed by the EDS results of the prepared ZnO nanorods, g-C3N4/ZnO, and GO/g-C3N4/ZnO. The outcomes indicated that the nanocomposites were highly uncontaminated and contained all necessary elements to facilitate the transformative process. The results of this experiment could be applied at a large scale, thus proving the effectiveness of photocatalysts for the removal of dyes.

Photocatalysis with nanostructured zinc oxide thin films: The relationship between morphology and photocatalytic activity under oxygen limited and oxygen rich conditions and evidence for a Mars Van Krevelen mechanism

Immobilised titanium dioxide (TiO2) in membrane structures has recently become attractive. This is due to the elimination of the separation step after the process of photocatalytic degradation. The efficiency of the TiO2 surface area exposed to UV light as the main important parameter needs to be considered. The immobilisation of TiO2 nanoparticles in the polyvinylidene fluoride (PVDF) membrane structure with different particle sizes (6 nm and 30 nm) was prepared via various techniques including the tape casting and spin coating methods to study the distribution of TiO2 nanoparticles in the membrane structure. Besides, the effects of the spinning speed in spin coating methods on the membrane structure and photocatalytic performance were investigated. The morphological and physical characteristics were also explored by field emission scanning electron microscope (FESEM) energy dispersion of X-ray (EDX), scanning electron microscopy (SEM) and atomic force microscopy (AFM) analysis. The prepared membranes were tested in a photocatalytic system using methylene blue (MB) as a model pollutant. The results showed that the immobilisation of TiO2 nanoparticles in membrane structure could enhance the rate of MB degradation. The aggregation of the 6 nm and 30 nm TiO2 particle sizes prepared by tape casting method shows similar performance in MB degradation rate but contradict the result of the spin coating method. The good distribution and uniformity of the 6 nm TiO2 particle size exhibit a higher MB degradation rate. The thickness of the membrane can be tailored using the spin coating method and UV penetration towards the photocatalytic membrane up to 55.64 μm of thickness, which could enhance the MB photocatalytic degradation rate.

As a result of their unique and novel properties, nanocomposites have found applications in a wide variety of fields. The purpose of this study is to demonstrate the ability to synthesize nanoparticles consisting of zinc oxide (ZnO) and graphene oxide (GO) via sol–gel techniques. An x‐ray diffractometer (XRD) as well as a UV–visible spectrometer were used to determine the crystalline and optical characteristics of the prepared samples. A hexagonal wurtzite crystal structure was observed in both pure ZnO nanoparticles and those that contain GO based on XRD results. It was estimated that the average crystallite size is based on the broadening of x‐ray lines. In comparison with pure ZnO, the antimicrobial properties were enhanced when GO was incorporated with ZnO. In addition, experiments on the absorption edge indicated the presence of a red shift as a result of the incorporation of GO. When GO is incorporated in quantitative amounts, the bandgap value of pure ZnO decreased. FTIR spectra exhibit a band of absorption at 486 cm−1, which confirms Zn‐O stretching in both samples. SEM images reveal a random pattern of structural features on the surface of the prepared samples. According to the EDX spectrum, pure GO nanoparticles and those doped with ZnO contain 61%–64% zinc and 32%–34% oxygen, respectively. When annealed at a higher temperature, ZnO NPs produced more H2 with a narrower bandgap than before annealing. In addition, methyl blue (MB) was used as an example of an organic compound in order to investigate the potential photocatalytic properties of nanoparticles with ZnO doped GO. In addition to DPPH assays, ZnO nanoparticles and ZnO doped GO nanoparticles were tested for their ability to scavenge free radicals. Comparing ZnO doped GO NPs with pure ZnO, these nanoparticles showed increased antioxidant activity. Based on the increased zone of inhibition observed for pure ZnO and ZnO doped GO (5, 10, 50, and 100 mg/mL), the antibacterial activity of pure ZnO and ZnO doped GO is concentration dependent. A detailed discussion of the results of the study demonstrated that ZnO doped GO and pure ZnO are toxic in different ways depending on how long they survive in degreased Zebrafish embryos and how fast they decompose.Research HighlightsThe scope of the manuscript was under the results of the study confirmed that both nanoparticles exhibited concentration dependent antioxidative activity.Determined that 89% of methyl orange dye can be degraded photocatalytically.ZnO nanoparticles were found to be 74.86% antioxidant at a concentration of 50 g/mL in the present study.At a concentration of 50 g/mL, ZnO doped GO NPs showed 79.1% antioxidant activity.Photocatalytic degradation mechanism scheme is implicit in the photoexcited charge carrier transportation path is observed for all the samples.Survival rate of zebrafish embryos was shown to decrease with increasing concentrations of ZnO and zinc oxide plus GO nanoparticles.

A scale‐up and sustainable method was developed to fabricate novel photocatalyst cellulose‐derived carbon aerogel@Na2Ti3O7 composite (CAT) by in situ growth of Na2Ti3O7 nanowhisker on the surfaces of fibers. With a three‐dimensional (3D) mesoporous network interconnected structure and a high specific surface area (248.92 m2/g), CAT exhibited excellent photocatalytic activity and methylene blue (MB) removal rate (98.3%). The photocatalytic experimental results showed that the CAT could degrade MB in the aqueous solution within 90 min. Compared with most reported catalysts, CAT exhibited a higher MB removal rate and shorter catalytic time. Therefore, the photocatalyst CAT based on environmentally friendly and low‐cost cellulose displayed great application potential in the degradation of MB.

In the present article, the synthesis of TiO2/diazonium/graphene oxide and its photocatalytic activity for methylene blue (MB) degradation have been demonstrated. The functionalization of graphene oxide (GO) with diazonium salt (diazonium-GO) was conducted for enhancing the dispersibility of GO in distilled water. TiO2 was highly dispersed in diazonium-GO to form TiO2/diazonium/graphene. The obtained specimens were characterized by X-ray diffraction, FT-IR spectroscopy, Raman spectroscopy, UV-Vis spectroscopy, scanning electron microscope, transmission electron microscopy, and X-ray photoelectron spectroscopy. It was found that the TiO2 phase in TiO2/diazonium/GO composites can be controlled by adjusting the amount of ethanol or titanium oxide in the reactant mixture. The obtained composites exhibited photocatalytic activities for methylene blue degradation (MB). The composite with ac. 70% anatase can provide the highest MB degradation efficiency. The studying of some intermediates for MB photocatalytic degradation using LC-MS showed that structure of MB by the cleavage and oxidation of one or more of the methyl group substituent on the amine groups lead to form compounds with low molecular masses. Total organic carbon studies confirmed a complete mineralization of MB. The present catalyst was stable and recyclable after three times with a negligible loss of catalytic activity. In addition, the TiO2/diazonium/GO can also photocatalyze for the degradation of some other dyes (phenol, methyl red, and Congo red).

The application of heterogeneous photocatalysis in industrial scale has been hindered by a lack of simple mathematical models that can be easily applied to reactor design and scale-up. This work intends to use a simple mathematical model for predicting methylene blue (MB) degradation in a slurry-annular photocatalytic reactor using zinc oxide (ZnO) hybridized with reduced graphene oxide (rGO)-ZnO composite. The mathematical model presented may be used as a tool to design, scale-up, and optimize annular photocatalytic reactors for water and wastewater treatment. A mathematical model for the photocatalytic degradation of MB with rGO-ZnO under UV light irradiation was developed. This model was achieved by combination of Langmuir–Hinshelwood kinetics and Lambert–Beer law. The accuracy of developed model was checked for predicting MB degradation in other operation conditions such as different photocatalyst dosage and initial MB concentration. On the basis of these results, the accuracy of the model was tested under different experimental conditions, resulting able to be predictive in different operating conditions.

Facile construction of ZnWO4/g-C3N4 heterojunction for the improved photocatalytic degradation of MB, RhB and mixed dyes

A cerium oxide nanoparticles (CeO2-NPs)/graphene oxide (GO)/polyacrylamide (PAM) ternary composite was synthesized through free-radical polymerization of acrylamide in the presence of CeO2 nanoparticles and GO in an aqueous system. The synthesized composite material was characterized by X-ray diffraction (XRD), Fourier transform infrared (FTIR) spectroscopy, scanning electron microscopy (SEM), and energy-dispersive X-ray (EDX) spectroscopy techniques and applied for the photocatalytic degradation of methylene blue (MB) dye from an aqueous solution. Tauc's model for direct transition was used to model for the optical band gap. The key operating parameters such as the amounts of CeO2-NPs and GO, pH, initial MB concentration, type of light irradiation, and contact time have been optimized to achieve the highest MB degradation percentage. The photocatalysis process was pH-dependent, and the optimum pH value was found to be 12.0. Under UV-A light, 90% dye degradation occurred in 90 min. The degradation of MB was also specified in terms of total organic carbon (TOC) and chemical oxygen demand (COD). Free-radical capture experiments were also performed to determine the role of radical species during the photocatalytic oxidation process. The photocatalytic process showed that the equilibrium data is in good agreement with the Langmuir-Hinshelwood kinetic model. A rate constant of 0.0259 min-1 was obtained. The hydrogel was also tested to assess its reusability, which is an important key factor in practical wastewater treatment. The photocatalytic activity only decreased to 75% after nine uses.

This paper is focused on obtained two catalysts such as TiO2 nanoparticles and Fe3O4/SiO2/TiO2 nanocomposite for adsorption and photocatalytic degradation of methylene blue (MB) dyes from aqueous solution. The morphology, structure and chemical proprieties of synthesized materials were investigated by X-ray diffraction (XRD) analysis, scanning electron microscopy (SEM), N2 adsorption-desorption isotherms and Zeta potential. The photocatalytic degradation of methylene blue under UV light in the presence of different synthesized catalysts was analyzed with Spectrometer UV-Vis. The photocatalytic degradation of methylene blue was studies by focusing of photoactivity performance of Fe3O4/SiO2/TiO2 in comparation with TiO2. An attempt has been made to study the effect of process parameters through amount of the catalysts and initial concentrations of methylene blue. In all cases was found that the kinetics of the MB photocatalytic degradation under UV light was fitted to the Langmuir–Hinshelwood. Even if the photocatalytic degradation study revealed that Fe3O4/SiO2/TiO2 and TiO2 degraded about 90 % of methylene blue within 60 min, the magnetic nanocomposite Fe3O4/SiO2/TiO2 serves as better catalyst compared with TiO2 nanoparticles. An important role in the photocatalytic degradation of MB is adsorption characteristic of TiO2 and Fe3O4/SiO2/TiO2 surface. The photocatalytic performance of Fe3O4/SiO2/TiO2 remained greater than TiO2 after 4 cycles of use.

More effective organics removal by amorphous MnOx assisted by micro-current than peroxymonosulfate addition: Performance and mechanism

Structure-directing ability of the kraft-lignin/cellulose carbon xerogel for the development of C-Nb2O5 sunlight-active photocatalysts

The zinc oxide (ZnO) nanostructures were synthesized using hydrothermal reaction technique at 180 °C with varying reaction time viz., 2, 4, 8 and 12 h and characterized with different spectroscopic/microscopic techniques. XRD indicate the formation of hexagonal phase of ZnO in all the prepared samples. The FESEM confirms the formation of hexagonal-shaped plate-like ZnO nanostructures having size in the range of 50 to 100 nm with the thickness of 10–15 nm, at 2 h reaction time. Further increase in the reaction time leads to increase in thickness of hexagonal ZnO plates resulting in formation of three-dimensional (3D) distorted spherical structures with facets. The photocatalytic activities were investigated by following degradation methylene blue (MB) dye. The ZnO prepared at 8 h of reaction time shows highest MB degradation rate, the apparent rate constant is 3.3 × 10–2 ± 0.1 × 10–2 min−1, almost five times more than 4 h reaction time. Photocatalytic dye degradation mechanism for two- & three-dimensional Zinc Oxide nanostructures on FESEM enlarge image of 8 h reaction time. Recycle study of MB degradation up to 5 recycles is shown (photographs of MB dye at time t0 and t120)