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In this study, we present a novel approach for the preparation of a highly ordered interconnected three-dimensional (3D) porous network structure of a silver atomic cluster (Ag@)/silver chloride photocatalyst using in situ precipitation 3D printing technique). The as-prepared photocatalyst structure exhibited high porosity and was tested for photocatalytic dye degradation and sterilization of Escherichia coli under visible and ultraviolet light irradiation. The results showed that the photocatalyst structure demonstrated strong degradation efficiency towards aqueous solutions of Orange II azo dye and methylene blue dye, and the kinetic properties followed a pseudo-first-order kinetics. The photocatalyst structure also exhibited efficient sterilization of E. coli, and the kinetics followed a pseudo-first-order and hyperbolic kinetics. Furthermore, after five cycles of dye degradation, the photocatalyst structure maintained high degradation rates of approximately 89.8% and 88.2% for Orange II azo and methylene blue dyes, respectively, indicating excellent durability and reliability of the prepared photocatalyst structure.

TiO 2 –FeZn nanocatalyst combined with sonolysis were used to activate peroxymonosulfate (PMS) as a highly efficient advanced oxidation process (US/TiO 2 –FeZn/PMS) for the decoloration of orange II dye (OII) and real textile wastewater. The characterization of the as-synthesized NPs was performed by SEM, FTIR, EDX and XRD analyses. Optimal experimental conditions of operational parameters were obtained: pH = 3, 15 mg/L initial OII concentration, 0.2 g/L PMS, 0.7 g/L nanocatalyst dosing, and 300 W ultrasonic power. The decolorization was observed to increase with increasing the dose of nanocatalyst and the ultrasonic power, and with decreasing pH (under acidic conditions). Under optimal experimental conditions, decolorization and COD removal of textile wastewater were 99.9% and 74.6%, respectively, at 40 min. The TiO 2 –FeZn/PMS/US as a novel process exhibited a higher removal of OII (95%) than TiO 2 NPs/PMS/US process (54%). The OII removal efficiency by the different processes decreased in the following order: TiO 2 –FeZn/US/PMS > TiO 2 –FeZn/PMS > TiO 2 –FeZn/US > TiO 2 /US/PMS > US/PMS > TiO 2 –FeZn > PMS > US. The recyclability study revealed that the process could be reused up to three consecutive cycles. The current US/nanocatalyst/PMS system was concluded to be an efficient, reusable and stable nanocatalyst for the oxidation of textile dyes.

Nb-Sn, V-Sn mixed-metal oxides and Nb-Si, V-Si metal oxide–silicas were successfully synthesized through a “soft” templating method, in which appropriate amounts of metal salts (either niobium(V) chloride, or vanadium(IV) oxide sulfate hydrate or tin(II) chloride dihydrate) or tetraethyl orthosilicate (TEOS) were mixed with hexadecyltrimethylammonium chloride (HDTA) or sodium dodecyl sulfate (SDS) solutions to obtain a new series of mesoporous oxides, followed by calcination at different temperatures. As-obtained samples were characterized by SEM, TEM, XRD, and UV-Vis spectra techniques. The photocatalytic activities of the samples were evaluated by degradation of methyl orange II (MO) under simulated sunlight irradiation. The effects of metal species and calcination temperature on the physicochemical characteristic and photocatalytic activity of the samples were investigated in detail. The results indicated that, compared to pure oxides, mixed-metal oxide showed superior photocatalytic performance for the degradation of MO. A maximum photocatalytic discoloration rate of 97.3% (with MO initial concentration of 0.6·10−4 mol/dm3) was achieved in 300 min with the NbSiOx material, which was much higher than that of Degussa P25 under the same conditions. Additionally, the samples were tested in the photochemical oxidation process, i.e., advanced oxidation processes (AOPs) to treat the commercial non-ionic surfactant: propylene oxide ethylene oxide polymer mono(nonylphenyl) ether (N8P7, PCC Rokita). A maximum of 99.9% photochemical degradation was achieved in 30 min with the NbSiOx material.

Banana peel-activated carbon (BPAC) with a very high surface area of 1,950 m 2  g −1 was prepared and investigated for the removal of methylene blue (MB) or Orange II dye molecules from aqueous solutions. Results of adsorption experiments showed that the BPAC exhibited high adsorption capacity with cationic dyes. The maximal Orange II and MB uptakes were determined to be more than 333 and 1,263 mg g −1 , respectively. The zeta-potential analysis revealed that surface charge of BPAC is negative and hence the present activated carbon is excellent for adsorption of MB cationic dye from water. The adsorption equilibrium, kinetics, and thermodynamics of MB dye were investigated and the results indicated a monolayer chemical adsorption involving electrostatic attraction. BPAC was found to be a highly promising material for the effective removal of cationic contaminants such as MB dye from water.

In recent years, the rapid development of industry has led to the discharge of large quantities of pollutants, including harmful dyes, into water sources, thereby posing potential threats to human health and the environment. FeOCl and biochar have their own shortcomings as a mediator in the heterogeneous Fenton process. To make both materials useful, FeOCl supported on bamboo biochar (FeOCl/BC) was prepared by calcination using FeCl3·6H2O and bamboo powder as raw materials, and the composite’s catalytic activities were explored with acid orange II (AO-II) as the target pollutant. The degradation efficiency of FeOCl/BC composites on AO-II was determined by testing the mass ratio of FeOCl and BC, initial pH, temperature, H2O2 concentration, catalyst addition, addition of coexisting inorganic anions, and natural organic matter. The addition of biochar to FeOCl increased the activation of H2O2 to generate •OH for the removal of AO-II and accelerated the cycle of Fe3+/Fe2+. The removal rate of AO-II by the Fe1C0.2 composite was 97.1% when the mass ratio of FeOCl and BC was 1:0.2 (Fe1C0.2), which was higher than that of the pure components (FeOCl or BC) at pH = 6.1. Moreover, after five reuses, the Fe1C0.2 composite still showed high degradation activity for AO-II, with 83.3% degradation and low activity loss. The capture experiments on the active material showed that the removal of AO-II by the Fe1C0.2 composite was mainly dominated by •OH; however, •O2− and h+ played minor roles. The synthesized Fe1C0.2 composite could be applied for organic contaminants such as AO-II with high removal efficiency.

This paper presents a study on orange II sodium salt (OII) degradation based on iron nanoparticles supported by kaolinite clays. The effects of nanoscale iron and initial dye concentration, as well as hydrogen peroxide dosage in a Fenton process, on the degradation of OII were studied. These nanoparticles were synthesized by green methods using coffee bean extract as a natural antioxidant for this process. Aqueous iron chloride was mixed with coffee extract, which is rich in antioxidants, and these antioxidants are responsible for the reduction of metal compounds into nanoparticles. The composite iron nanoparticle-kaolinite composite was synthesized from an aqueous FeCl3 and kaolinite solution with the added coffee bean extract. The results showed that OII removal efficiency increased with the amount of iron nanoparticles (n-Fe) alone and with the amount iron-supported-kaolinite composite. By increasing the amount of composite, the adsorptive surface area increases as well as the number of active sites, which determine the higher removal efficiency. Regarding H2O2 dosage, dye removal was more efficient at lower quantities: 62% removal efficiency with addition of 10 mL H2O2, while for the test conducted with 20 mL H2O2, removal efficiency was 47%. A possible reason for this behavior can be the n-Fe/ H2O2 ratio, which influences the production of degradation products and hinders the degradation.Highlights• Green synthesized metallic iron nanoparticles (n-Fe) using coffee bean extract as a natural oxidant were used for the removal of Orange II• In order to improve the degradation process, a clay-nanoscale iron composite was used, as well as Fenton oxidation using added H2O2. As a support material for the composite, kaolinite was used. The results showed that both reduction and adsorption processes are involved in the dye removal process. Applying Langmuir and Freundlich isothermal models shows monolayer coverage• By comparing the efficiency of the composite alone with the efficiency of the composite with the Fenton process, better results were obtained for the second case which shows the importance of the H2O2/Fe system in the degradation process. Also, we may state that the best results were obtained by using n-Fe only• Since the amount of n-Fe present in the composite is low (0.01 g), further experiments should be held concerning the ratios between n-Fe and clay in the composite. Experiments using wastewater containing dyes from a real industrial process should also be done as well, to confirm the activity of this material containing nanoscale iron made using green synthesis in a real wastewater environment, with all the associated ions and compounds.

The doping of Au/TiO2 with FeOx is shown to result in a strong enhancement of its photocatalytic activity in the degradation of the azo dye Orange II. In order to examine the source of this enhancement, Au-FeOx/TiO2 nanocomposites containing different molar ratios of Au:Fe were synthesized, and X-ray diffraction (XRD), X-ray photoemission spectroscopy (XPS), and high-resolution transmission electron microscope (HRTEM) analyses indicated that the TiO2-supported Au nanoparticles were partially covered with an amorphous layer of FeOx species, in which the iron was present as Fe2+ and Fe3+. The metal-semiconductor system, i.e., Au/TiO2, showed only a moderate degradation rate, whereas doping with FeOx strongly enhanced the degradation activity. The bandgap energy decreased gradually from Au/TiO2 (3.13 eV) to the catalyst with the highest FeOx loading Au-FeOx (1:2)/TiO2 (2.23 eV), and this decrease was accompanied by a steady increase in the degradation activity of the catalysts. XPS analyses revealed that compared to Au/TiO2, on Au-FeOx/TiO2 a much higher population density of chemisorbed and/or dissociated oxygen species was generated, which together with the decreased bandgap resulted in the highest photocatalytic activity observed with Au-FeOx (1:2)/TiO2. The processes occurring during reaction on the catalyst surface and in the bulk liquid phase were investigated using operando attenuated total reflection IR spectroscopy (ATR-IR) combined with modulation excitation spectroscopy (MES), which showed that the doping of Au/TiO2 with FeOx weakens the interaction of the dye with the catalyst surface and strongly enhances the cleavage of the azo bond.

The photocatalytic activities of two samples of α-Fe 2 O 3 nanoparticles have been evaluated. One sample has been synthesized by a precipitation method with oxalic acid (soft method), and the other sample has been produced with the aid of a hard template (nanocasting with silica). The photodegradation of azo dye Orange II ( OII ), a model water pollutant, has been used as a benchmark reaction. It has been found that the synthetic method has a deep effect on the photocatalytic activity of the tested hematites, since sample created with the soft method is notably more photoactive than the one made with nanocasting procedure (k = 8.9 × 10 − 3  min −1 vs. k = 1.6 × 10 −3  min −1 respectively) when irradiated with UV light. Similar higher activity of the soft method sample has been found when visible light was used as excitation source (k = 8.3 × 10 −3  min −1 vs. k = 0.4 × 10 −3  min −1 respectively). The enhanced surface adsorption of OII on the sample prepared via the soft methodology, which is ten times higher than the adsorption on sample prepared via the nanocasting path, could explain the better photocatalytic performance of the former material. Graphical Abstract

A novel calcium alginate (SA/Ca) gel pellet adsorbent was prepared by ion exchange reaction and polymerization between sodium alginate (SA) and Ca2+ in the solution, and characterized by SEM, EDS, FTIR and XRD. Taking acid orange II ( AO II) dye as the adsorption object, the influence of some important conditions about preparation and adsorption on SA/Ca properties was discussed in detail. The adsorption kinetics were studied. The results show that SA/Ca adsorbent has good adsorption effect on AO II dye under the conditions of the mass concentration ratio 2 : 5 of SA and CaCl2 solutions and reaction time of 2h at 25°C. When the adsorbent dosage is 4g/L and initial dye concentration of natural pH is 1000 mg/L, the adsorption equilibrium can basically reach in 180 min at 25°C with the adsorption capacity of 225mg/g and more than 90% of removal efficiency. The adsorption kinetics fully fit pseudo-second order model. The characterization results indicate that the SA powder is composed of various irregular particles, while dry SA/Ca solid are all pellets with diameter of about 1mm. The surface of inhomogeneous spheres is stacked with obstacles, and folds and ravines coexist. Ca2+ and most Na+ in SA molecule carried out ion exchange and formed a stable network-structure polymer SA/Ca gel pellets, which can effectively remove acid dyes from wastewater, and are easy to be separated after adsorption. As a biopolymer adsorbent with simple preparation method, environmental friendliness and non-toxic side effects, SA/Ca has good development potential and application prospects.

A series of Mo-doped ZnO photocatalysts with different Mo-dopant concentrations have been prepared by a grind- ing-calcination method. The structure of these photocatalysts was characterized by a variety of methods, including N2 physical adsorption, X-ray diffraction （XRD）, scanning electron microscopy （SEM）, Fourier transform infrared （FT-IR） spectroscopy, photoluminescence （PL） emission spectroscopy, and UV-vis diffuse reflectance spectroscopy （DRS）. It was found that Mo6＋ could enter into the crystal lattice of ZnO due to the radius of MO6＋ （0.065 nm） being smaller than that of Zn2＋ （0.083 nm）. XRD results indicated that Mo6＋ suppressed the growth of ZnO crystals. The FT-IR spectroscopy results showed that the ZnO with 2 wt.% Mo-doping has a higher level of surface hydroxyl groups than pure ZnO. PL spectroscopy indicated that ZnO with 2 wt.% Mo-doping also exhibited the largest reduction in the intensity of the emission peak at 390 nm caused by the recombi- nation of photogenerated hole-electron pairs. The activities of the Mo-doped ZnO photocatalysts were investigated in the pho- tocatalytic degradation of acid orange II under UV light （2 = 365 nm） irradiation. It was found that ZnO with 2 wt.% Mo-doping showed much higher photocatalytic activity and stability than pure ZnO. The high photocatalytic performance of the Mo-doped ZnO can be attributed to a great improvement in the surface properties of ZnO, higher crystallinity and lower recombination rate of photogenerated hole-electron （e-/h＋） pairs. Moreover, the undoped Mo species may exist in the form of MoO3 and form MoO3/ZnO heterojunctions which further favors the separation of e/h＋ pairs.