High Throughput Analysis of Photocatalytic Water Purification

A novel synthesis of graphene oxide-titanium dioxide (GO-TiO2) and graphene oxide-zinc oxide (GO-ZnO) nanocomposites and their application as effective, reusable photocatalysts for degradation of methylene blue (MB) dye

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.

Ecofriendly and low-cost synthesis of ZnO nanoparticles from Acremonium potronii for the photocatalytic degradation of azo dyes

Nanoparticles (NPs) have enormous applications in every field of science by their particular size, diverse morphology, and higher surface-ratio, which provide them for unique properties. Nanosized materials can be used to overcome almost every challenge in science. The development of nanoscience, metal or metal oxide NPs have emerged as promising materials. Especially, zinc oxide nanoparticles (ZnO NPs) have remarkable applications in diverse fields including cosmetic, optical, and electrical fields, biomedicine, and catalysis. Several cost-effective strategies using different chemicals, plants, and microbes mediated ZnO NPs are reported in several studies, among which fungal-mediated approaches have gained tremendous interest due to their eco-friendly and simple protocols. In this study, we report the formation of ZnO NPs with sizes ranging between 13 and 15 nm using Acremonium potronii, a new fungal species found in fruits, soil, and marine environments. The obtained ZnO NPs are characterized by several analytical techniques, and their catalytic activity in the degradation of methylene blue dye is investigated, including a kinetic study to investigate the rate of degradation process. The ZnO NPs can degrade about 93% of the dye. This work demonstrates the potential of the synthesized ZnO NPs as dye removal catalysts and offers a platform for the application of A. potronii.

Photocatalytic Activity of Graphene Oxide/Zinc Oxide Nanocomposites with Embedded Metal Nanoparticles for the Degradation of Organic Dyes

Nanocomposite materials based on metal nanoparticles and graphene oxide (GO) have gained increasing attention for their wide range of potential applications in various materials science fields. In this study, an efficient photocatalyst based on GO/ZnO nanocomposites with embedded metal nanoparticles was successfully synthesized via a simple one-pot method. The synthesized nanocomposites were characterized using X-ray diffraction (XRD), scanning electron microscopy (SEM), and Fourier transform infrared (FTIR) spectroscopy. The photocatalytic activity of the synthesized nanocomposites was tested in the degradation of methylene blue (MB) dyes, as a model of water pollutants. A catalytic activity of 84% was achieved using a nanocomposite with a percentage of 3.125% GO, after 90 min sunlight irradiation. Furthermore, embedded copper and silver nanoparticles were used as dopants to study their effects on the activity of the photocatalyst. The GO-ZnO-Cu nanocomposite showed that the activity toward MB degradation was decreased by 50%, while a significant increase in the activity of MB degradation was achieved by the GO-ZnO-Ag nanocomposite. The removal efficiency of MB by the GO-ZnO-Ag nanocomposite reached 100% after 40 min of sunlight irradiation. Thus, the GO-ZnO-Ag nanocomposite has the potential to be an efficient adaptable photocatalyst for the photodegradation of organic dyes in industrial wastewater.

High-throughput analysis of photocatalytic reactivity of differing TiO2 formulations using 96-well microplate reactors

The rapid development of photocatalysts for water decontamination benefits from availability of sensitive platforms for screening photocatalytic reactivity. The standard approach typically involves quantifying the degradation of a single dye compound in a slurry system in individual beakers, which requires tedious photocatalyst separation and long operation time. We present a simple and efficient method for assessing the photocatalytic activity of different photocatalyst nanomaterials that eliminates the solid separation process. The 96-well microplate method demonstrated an improved applicability as a high-throughput screening method for photocatalytic reaction mechanisms using a wide range of chemical substrates (i.e., methyl orange, methylene blue, terephthalic acid, and β-nicotinamide adenine dinucleotide coenzyme) and photocatalyst concentrations (1-100 mg/L). By employing photocatalysts at lower concentrations compared to the slurry system, rapid screening was accomplished through direct spectrophotometric or spectrofluorometric measurements. The mass-normalized rate constants of dye degradation were used to determine the photocatalytic reactivity of three commercial TiO₂ nanomaterials, which followed an order of SRM TiO₂ 1898 ≈ Degussa TiO₂ P90 > Food-grade TiO₂ E171. The extent of hydroxyl radical involvement in methyl orange degradation was estimated to be ∼74% by using radical scavengers in the microplate reactor. Given the utilization of low-concentration photocatalyst, this protocol may be used for evaluating photocatalytic reactivity and oxidative stress caused by photocatalyst exposure in an aquatic environment. We further evaluated photocatalytic reaction kinetics with respect to energetic and photonic efficiency. The method could greatly facilitate comparisons across different laboratories when quantifying photocatalytic reactivity and efficiency, which would aid in standardizing bench-scale photocatalysis testing.

Inorganic Membranes: Preparation and Application for Water Treatment and Desalination

Inorganic membrane science and technology is an attractive field of membrane separation technology, which has been dominated by polymer membranes. Recently, the inorganic membrane has been undergoing rapid development and innovation. Inorganic membranes have the advantage of resisting harsh chemical cleaning, high temperature and wear resistance, high chemical stability, long lifetime, and autoclavable. All of these outstanding properties made inorganic membranes good candidates to be used for water treatment and desalination applications. This paper is a state of the art review on the synthesis, development, and application of different inorganic membranes for water and wastewater treatment. The inorganic membranes reviewed in this paper include liquid membranes, dynamic membranes, various ceramic membranes, carbon based membranes, silica membranes, and zeolite membranes. A brief description of the different synthesis routes for the development of inorganic membranes for application in water industry is given and each synthesis rout is critically reviewed and compared. Thereafter, the recent studies on different application of inorganic membrane and their properties for water treatment and desalination in literature are critically summarized. It was reported that inorganic membranes despite their high synthesis cost, showed very promising results with high flux, full salt rejection, and very low or no fouling.

High throughput screening of photocatalytic conversion of pharmaceutical contaminants in water

The susceptibility for photon-induced degradation of over 800 pharmaceutical compounds present in the LOPAC¹²⁸⁰ library, was analyzed by UV/Vis spectroscopy in the absence or presence of TiO₂ P25 in water. In general, few compounds were effectively degraded in the absence of the TiO₂ photocatalyst (3% of all compounds tested), while in the presence of TiO₂, the majority of compounds was converted, often to a large degree. Differences in degree of degradation are evaluated on the basis of molecular weight, as well as the chemical nature of the drug compounds (functional groups and pharmacological classes). In general, if the molecular weight increases, the degradation efficacy decreases. Relatively high degrees of conversion can be achieved for (relatively small) molecules with functional groups such as aldehydes, alcohols, ketones and nitriles. A low degree of conversion was observed for compounds composed of conjugated aromatic systems. Trends in degradation efficacy on the basis of pharmacological class, e.g. comparing hormones and opioids, are not obvious.

Fabrication of Au/graphene-wrapped ZnO-nanoparticle-assembled hollow spheres with effective photoinduced charge transfer for photocatalysis

Heterostructures of gold-nanoparticle-decorated reduced-graphene-oxide (rGO)-wrapped ZnO hollow spheres (Au/rGO/ZnO) are synthesized using tetra-n-butylammonium bromide as a mediating agent. The structure of amorphous ZnO hollow spheres is found to be transformed from nanosheet- to nanoparticle-assembled hollow spheres (nPAHS) upon annealing at 500 °C. The ZnO nPAHS hybrids with Au/rGO are characterized using various techniques, including photoluminescence, steady-state absorbance, time-resolved photoluminescence, and photocatalysis. The charge-transfer time of ZnO nPAHS is found to be 87 ps, which is much shorter than that of a nanorod (128 ps), nanoparticle (150 ps), and nanowall (990 ps) due to its unique structure. The Au/rGO/ZnO hybrid shows a higher charge-transfer efficiency of 68.0% in comparison with rGO/ZnO (40.3%) and previously reported ZnO hybrids. The photocatalytic activities of the samples are evaluated by photodegrading methylene blue under black-light irradiation. The Au/rGO/ZnO exhibits excellent photocatalytic efficiency due to reduced electron-hole recombination, fast electron-transfer rate, and high charge-transfer efficiency.