Photocatalytic Degradation Of Water Pollutants Research Articles

High performance magnetically recoverable g-C3N4/Fe3O4/Ag/Ag2SO3 plasmonic photocatalyst for enhanced photocatalytic degradation of water pollutants

The g-C3N4/Fe3O4/Ag/Ag2SO3 nanocomposites have been successfully fabricated by facile refluxing method. The as-obtained products were characterized by XRD, EDX, SEM, TEM, UV–vis DRS, FT–IR, TGA, PL, and VSM techniques. The results suggest that the Ag/Ag2SO3 nanoparticles have anchored on the surface of g-C3N4/Fe3O4 nanocomposite, showing strong absorption in the visible region. The evaluation of photocatalytic activity indicates that for the g-C3N4/Fe3O4/Ag/Ag2SO3 (40%) nanocomposite, the degradation rate constant was 188×10−4min−1 for rhodamine B, exceeding those of the g-C3N4 (16.0×10−4min−1) and g-C3N4/Fe3O4 (20.2×10−4min−1) by factors of 11.7 and 9.3, respectively. The results showed that the nanocomposite prepared by refluxing for 120min has the superior photocatalytic activity and its activity decreased with rising the calcination temperature. The trapping experiments confirmed that superoxide ion radical was the main active species in the photocatalytic degradation process. Also, it was demonstrated that the magnetic photocatalyst has considerable activity in degradation of one more dye pollutant. Finally, the reusability of the photocatalyst was evaluated by five consecutive catalytic runs. This work may open up new insights into the utilization of magnetically separable nanocomposites and provide new opportunities for facile fabrication of g-C3N4-based plasmonic photocatalysts.

A unique nanoporous graphene-ZnxCd1−xS hybrid nanocomposite for enhanced photocatalytic degradation of water pollutants

In this work, a novel in-situ solvothermal reduction route has been made to immobilize nanoporous ZnxCd1−xS aggregates on graphene nanoribbons by using PVP as a stabilizer and thiourea as a sulphur source. The nanoporous ZnxCd1−xS aggregates with diameters of 20–30nm assembled from ZnxCd1−xS nanocrystals (3–5nm) are homogeneously anchored on graphene nanoribbons and the unique structure of graphene-ZnxCd1−xS nanocomposites has contributed to large specific surface area (102.1m2g-1). Despite the analogous size and configuration, the nanoporous graphene-ZnxCd1−xS hybrid nanocomposites exhibited composition-dependent photocatalytic performances for the degradation of methyl orange (MO) under visible light. In particular, graphene-Zn0.5Cd0.5S was capable of nearly completely degrading MO in 150min. The excellent photocatalytic activity was proposed to arise from the synergy effect between nanoporous ZnxCd1−xS aggregates and graphene, the suitable band gap, intimate interfacial contact, and unique nanoporous structure. Moreover, the work provides a simple strategy to prepare various nanoporous graphene-semiconductor nanocomposites.

Simple synthesis of anatase/rutile/brookite TiO2 nanocomposite with superior mineralization potential for photocatalytic degradation of water pollutants

In this study, we report a simple synthesis procedure of anatase/rutile/brookite TiO2 nanocomposite material, designed for efficient transformation of emerging water pollutants (e.g., bisphenol (A)) to CO2 and H2O as final products of complete photo-oxidation. Sol–gel procedure with a subsequent hydrothermal treatment carried out at mild temperature and in the presence of 3M HCl led to the formation of TiO2 nanomaterial, which consists of anatase (43%), rutile (24%) and brookite (33%) polymorph phases within the same material. For the purpose of efficient evaluation of nanocomposite activity, individual polymorphs of anatase, rutile and brookite were also prepared using the same precursor material. Individual polymorph phases within the nanocomposite material crystallized separately and formed mixed agglomerates; the polymorphs were regularly shaped and randomly distributed in agglomerates, where some of the anatase particles exhibited truncated octahedron morphology, rutile was in the form of tetragonal prisms with pyramidal termination and brookite was shaped as blocky particles, which were found to be the smallest within the nanocomposite material (∼20nm). Newly synthesized TiO2 nanocomposite was highly active in terms of mineralization, since after 60min of irradiation under UV light almost 60% of water dissolved pollutant bisphenol A was successfully transformed into CO2 in H2O. On the other hand, the benchmark TiO2 P25 Degussa catalyst reached a lower extent of mineralization, which is due to significantly less expressed resistance to accumulation of carbonaceous deposits on the catalyst surface.

Synthesis, characterisation and application of TiO2–zeolite nanocomposites for the advanced treatment of industrial dye wastewater

Photocatalysis usually involves the utilisation of nano-sized semiconductor photocatalysts owing to their higher specific surface area and surface reaction rate. However, the key challenges in the utilisation of nano-sized photocatalysts for advanced treatment of industrial dye wastewater are to enhance the post-separation and recovery of spent photocatalysts to prevent them from diffusing into the environment. Thus, the main aim of this study was to synthesize a functional-form of titanium dioxide (TiO2)–zeolite nanocomposite through the modified two-step sol–gel method for enhanced application and separation after advanced industrial dye wastewater treatment. The synthesized TiO2–zeolite nanocomposite was characterised using field-emission scanning electron microscopy (FE-SEM), energy dispersive X-ray (EDX) analysis, Fourier-transformed infrared spectroscopy (FTIR), particle size distribution analysis and Brunauer–Emmett–Teller (BET) specific surface area and porosity analysis. Subsequently, the photoactivity of synthesized TiO2–zeolite nanocomposite was measured and compared against the commercial TiO2 particles. It was found that the TiO2–zeolite nanocomposite shows a high apparent pseudo-first order reaction rate constant of 0.0419 min−1 at lower dye concentration. This showed that the synthesized TiO2–zeolite nanocomposite follows a more adsorption-oriented photocatalytic degradation of water pollutants, which is useful for removing trace and untreated dye compounds in the advanced industrial dye wastewater treatment stage.

Effective quantum yield and reaction rate model for evaluation of photocatalytic degradation of water contaminants in heterogeneous pilot-scale solar photoreactors

A generalized model for the evaluation of solar photocatalytic degradation of water pollutants in heterogeneous pilot-scale solar photoreactors using slurry suspensions of TiO2-P25 is presented. The model is developed through the coupling of a modified rate equation derived from a Langmuir–Hinshelwood kinetic approach and a new model of “effective” quantum yield which is based explicitly on the optical properties of the catalyst and on the incident photon flux, but independent of the composition of the reactants in solution. The model was validated experimentally in three pilot-scale, compound parabolic collectors (CPCs) of different length. The kinetic parameters obtained from this new model are intrinsic to the nature of the reagent system. The results show that this approach is applicable to other photocatalytic degradation systems and is independent of the operating conditions, the geometry and the scale of the reactor. The model could also predict quantum yields of the photocatalytic degradation of 1,4-dioxane, hormone disrupting estrogens (E1, E2, EE2, E3), propanal, dichloroacetic acid, phenol, chlorophenols, methylphenols, 2,4-dichlorophenoxy-acetic acid (2,4-D), diuron and ametryne in single and multicomponent systems.

Use of ordered mesoporous titania with semi-crystalline framework as photocatalyst

The photocatalytic degradation of water pollutants using highly ordered mesoporous TiO2 particles is an emerging area of environmental remediation. Titania particles with a high hexagonal mesopore ordering and a large surface area have been synthesized by a new surfactant templating process that combined both the evaporation-induced self assembly method and the liquid crystal templating pathway. The transformation of the amorphous titanium dioxide walls into nanosized anatase walls is obtained by calcination. The photocatalytic oxidation of methyl orange has been investigated in mesoporous TiO2 aqueous suspensions irradiated by artificial UV-light. The effect of some physicochemical parameters such as time of adsorption prior to UV irradiation, initial methyl orange concentration, photonic flux, pH and amount of photocatalyst has been analyzed in details to optimize the experimental parameters. The efficiency of the process depends on the working conditions and the optimal conditions are: 1h of dark adsorption, a TiO2 concentration of 0.5g/L, an initial methyl orange concentration of 15mgL−1 at acidic pH (pH 4) with an incident light intensity of 10−5EinsteinL−1s−1. The rates of methyl orange decomposition follow Langmuir–Hinshelwood kinetics. The dependence of the reaction rate on the incident light intensity is first order. The reproducibility of the mesoporous TiO2 as photocatalyst for methyl orange degradation is investigated during several cycles experiments. No change in the activity of the catalyst is observed at the first 4 cycles which indicates that the TiO2 is able to use repeatedly.

Selective photocatalytic degradation of aquatic pollutants by titania encapsulated into FAU-type zeolites

The selective photocatalytic degradation of charged pollutants in water was achieved on titania encapsulated into FAU-type zeolites. The electrostatic attraction of cationic substrates and repulsion of anionic substrates by the negatively charged zeolite framework facilitated the selective photocatalytic degradation of charged substrates. The hybrid zeolite–titania photocatalysts were prepared through the ion-exchange method. The titania clusters were mainly well distributed within the cavities of FAU-type zeolites whereas no TiO 2 nanoparticles aggregates were observed on the external surface of zeolite crystals. The hybrid zeolite–titania photocatalysts were characterized by diffuse reflectance UV–visible spectroscopy, transmission electron microscopy, energy-dispersive X-ray analysis and X-ray photoelectron spectroscopy. The selective degradation of charged pollutants was investigated by employing three pairs of oppositely charged substrates. The comparison between the cationic and anionic substrates clearly showed that the degradation rates for the cationic substrates on the hybrid photocatalysts are markedly higher than those for the anionic substrates. Among the cationic substrates, the smaller cations such as tetramethylammoniums were preferentially degraded. This enabled the selective removal of cationic substrates among the mixture. Such a selective photocatalytic degradation of water pollutants may provide a useful strategy for the development of economical photocatalytic process by targeting only the most recalcitrant pollutant.

A novel scheelite-like structure of BaBi 2Mo 4O 16: Photocatalysis and investigation of the solid solution, BaBi 2Mo 4− xW xO 16 (0.25 ≤ x ≤ 1)

A barium bismuth molybdate, BaBi 2Mo 4O 16, was synthesized for the first time. The compound was made by the solid-state technique and studied for photocatalytic degradation of water pollutants. The compound crystallizes in the monoclinic C2/ c system with a = 5.317 (1) Å, b = 12.875 (2) Å, c = 19.390 (3) Å, β = 101.512 (4)°, V = 1327.1 (4) Å 3 and Z = 4. The crystal structure along the a-axis consists of layers of [Bi 2O 2] units and BaO 10 polyhedra both surrounded by isolated MoO 4 tetrahedra representing a scheelite-like structure. Photocatalytic degradation of phenols and substituted phenols, acids and dyes were studied using BaBi 2Mo 4O 16 as catalyst. The catalyst shows selectivity towards chlorine containing aromatics. Substitution of tungsten for molybdenum resulted in retention of structure within the limits 0.25 ≤ x ≤ 1 of the solid solution, BaBi 2Mo 4− x W x O 16. The phases, x = 0.25, 0.50, 0.75 and 1.0, in the solid solution were also used to study the photocatalytic degradation of water pollutants like phenol, substituted phenols and dyes. The photocatalytic activity increases slightly with an increase in substitution of tungsten in the solid solution domain.

Titanium dioxide sol–gel deposited over glass and its application as a photocatalyst for water decontamination

Photocatalytic degradation of water pollutants using TiO 2 and solar light has been proposed as an effective alternative of treatment. Usually, TiO 2 as a finely divided powder is added to polluted water forming a suspension, which is then irradiated under sunlight to conduct photochemical reactions. Although the literature frequently points out the minor efficiency of immobilized systems, it is desirable to look for a fixed catalyst to avoid wastes of time and materials during separation of the powder at the end of the treatment. This paper presents results that show the use of anatase thin films as an efficient form of deposited TiO 2 for the photocatalytic degradation of 4-chlorophenol, a priority pollutant commonly used as a model in photocatalysis, and for carbaryl, a carbamic pesticide. The thin films were deposited over small cylindrical pieces of glass, using a sol–gel technique, the average thickness being 600 nm, and having a band gap of 3.28 eV. The anatase TiO 2-covered glasses were used to fill a cylindrical photoreactor located at the focus of a parabolic solar collector able to concentrate up to 41 suns. Results show that the films are an effective catalyst in photodegradation, under solar irradiation, and conduct to similar values as those for TiO 2 in suspension. The photoefficiency obtained is similar to that obtained using powder suspension. These results compel us to the continued pursuit of TiO 2 immobilization.

Efficient Photocatalytic Degradation of Environmental Pollutants with Mass-Produced ZnS Nanocrystals

Photocatalytic degradation of water pollutants using nanometersized semiconductor colloids is an emerging area of environmental remediation. The synthesis of semiconductor nanocrystals (NCs), however, can be costly and result in low product yields. For large-scale photocatalytic application in environmental remediation, cost-effective production of the semiconductor NCs would be ideal. Demonstrated in this report is the efficient photocatalytic degradation of p-nitrophenol (pNP) and Acid Orange 7 (AO7) using ZnS nanocrystals (∼3 to 5 nm diameter) produced in gram quantities with >50% product yield. The pNP half-life in ZnS nanocrystal photocatalyzed reactions was about 1.95 to 2.45 min, whereas in comparable TiO2 reactions, the pNP half-lives were in the range of 12 to 15 min. Absorption spectra of the photocatalysis reactions suggested the decolorization of pNP without any noticeable formation of phenolic intermediates, implying a mechanism that involves a pNP ring opening via a radical mediated attack. Likewise, the degradation of AO7 was suggested to occur via an oxidative pathway involving hydroxyl radicals formed at the photocatalyst/liquid interface. Optimum conditions for AO7 degradation such as pH, photocatalyst-to-AO7 ratio, and photocatalyst surface passivation were similar to those for pNP. By demonstrating efficient mineralization of these model pollutants using mass-produced ZnS nanocrystals, we hope to lay the foundations necessary for development of large-scale, field-applicable systems.