Two novel MOFs@COFs hybrid-based photocatalytic platforms coupling with sulfate radical-involved advanced oxidation processes for enhanced degradation of bisphenol A.

Nowadays, the visible-light-driven photocatalysis via advanced photocatalyst for PS activation have promising applications in wastewater treatment. Herein, for the first time, two novel MOFs@COFs hybrid materials (denoted as MIL-101-NH2@TpMA and UiO-66-NH2@TpMA) with nitrogen-rich building blocks were fabricated via a feasible step-by-step assembly method, and then employed as efficient photocatalytic platform coupling with sulfate radical-based advanced oxidation processes for the degradation of BPA under visible light irradiation. Detailed analyses revealed that the hybridization of MOFs and COFs could greatly boost visible light absorption, while the heterojunction formed at the interface could effectively facilitate the separation and transfer of photogenerated electron-hole pairs. More importantly, the developed solar/MOFs@COFs/PS system exhibited the excellent degradation ability toward BPA, and an incredible degradation efficiency of 99% was eventually achieved. Possible mechanism for photocatalytic degradation of BPA was also proposed. Furthermore, the prepared composites with great reusability and stability possessed a broad potential for highly effective degradation of various organic contaminants. In short, this work not only demonstrated the combination of MOFs and COFs with C3N4 active unit was a feasible strategy for improving photocatalytic activities in the degradation of organic contaminants, but also provided some novel inspirations for constructing high-efficient photocatalysts with heterostructure.

Impacts of sulfidation of silver nanowires on the degradation of bisphenol A in water.

Silver nanowires (AgNWs) are widely produced in many electronic and optical products, and could be inevitably discharged into the aquatic environments. Sulfidation is one of the most important transformation processes of AgNWs, and could significantly affect their fate and interactions with other pollutants in aquatic environment. In the present study, the sulfidation products of AgNWs with different atomic ratio of Ag and S were prepared under environmentally relevant conditions. The crystal structure, elemental composition, morphology and size of the sulfidation products were comprehensively characterized by powder X-ray diffraction, UV-vis spectroscopy, X-ray photoelectron spectroscopy and transmission electron microscope. The products were heterostructured nanowires and the Ag2S/Ag molar ratio increased with extension of the reaction time. The produced Ag2S-Ag nanowires displayed a good photocatalytic activity and facilitated the degradation of the copresent organic pollutant bisphenol A (BPA) under simulated sunlight irradiation. As sulfidation time increased, more Ag2S was generated and the Ag2S-Ag composites displayed high promotion effect on BPA degradation. This effect could be ascribed to the favorable synergistic effects between Ag2S and AgNWs, such as high electron-hole separation efficiency and low charge transfer resistance. The chemical scavenger experiments demonstrated that superoxide anion radicals and photogenerated holes in the sulfidation products of AgNWs could be the main reactive species for photocatalytic degradation.

Excellent Temperature-Control Based on Reversible Thermochromic Materials for Light-Driven Phase Change Materials System.

Light-driven phase change materials (PCMs) have received significant attention due to their capacity to convert visible light into thermal energy, storing it as latent heat. However, continuous photo-thermal conversion can cause the PCMs to reach high thermal equilibrium temperatures after phase transition. In our study, a novel light-driven phase change material system with temperature-control properties was constructed using a thermochromic compound. Thermochromic phase change materials (TC-PCMs) were prepared by introducing 2-anilino-6-dibutylamino-3-methylfluoran (ODB-2) and bisphenol A (BPA) into 1-hexadecanol (1-HD) in various proportions. Photo-thermal conversion performance was investigated with solar radiation (low power of 0.09 W/cm2) and a xenon lamp (at a high power of 0.14 W/cm2). The TC-PCMs showed a low equilibrium temperature due to variations in absorbance. Specifically, the temperature of TC-PCM180 (ODB-2, bisphenol A and 1-HD ratio 1:2:180) could stabilize at 54 °C approximately. TC-PCMs exhibited reversibility and repeatability after 20 irradiation and cooling cycles.

Degradation of bisphenol a using peroxymonosulfate activated by WO3@MoS2/Ag hollow nanotubes photocatalyst.

WO3@MoS2/Ag (HW@MA) hollow tubes were successfully engineered to photodegrade bisphenol A (BPA) combined with peroxymonosulfate (PMS) for the first time. XRD, XPS, TEM and SEM were conducted. The HW@MA tubes present excellent photocatalytic performance on the removal of BPA. The intermediate products of BPA were investigated by GC-MS analysis and the degradation pathway was proposed. To explore the transferred mechanism of photoproduced carriers, the electron paramagnetic resonance (EPR) technique was carried out. The results revealed that the superoxide radical (O2-), hydroxyl radical (OH), sulfate radical (SO4-) were the main active radicals. Moreover, the formed schottky junctions enhanced the separation efficiency of photoinduced electron-hole pairs. Besides, the effect of the photocatalysts' dosage, PMS concentration, pH of the initial solution and co-existing anions on the BPA degradation were investigated.

Effect of nitrate, carbonate/bicarbonate, humic acid, and H2O2 on the kinetics and degradation mechanism of Bisphenol-A during UV photolysis.

In this study, the effects of natural water components (nitrate, carbonate/bicarbonate, and humic acid) on the kinetics and degradation mechanisms of bisphenol A (BPA) during UV-C photolysis and UV/H2O2 reaction were examined. The presence of NO3- (0.04-0.4 mM) and CO32-/HCO3- (0.4-4 mM) ions increased BPA degradation during UV photolysis. Humic acid less than 3 mg/L promoted BPA degradation, but greater than 3 mg/L of humic acid inhibited BPA degradation. During the UV/H2O2 reaction, all water matrix components acted as radical scavengers in the order of humic acid > CO32-/HCO3- > NO3-. All of the degradation reactions agreed with the pseudo-first-order kinetics. While eight byproducts (m/z = 122, 136, 139, 164, 181, 244, 273, 289) were identified in UV-C/NO3- photolysis reaction, four (m/z = 122, 136, 164, 244) and three byproducts (m/z = 122, 136, 164) were observed during UV-C/NO3-/CO32-/HCO3- and UV-C/CO32-/HCO3- reactions. Nitrogenated and hydrogenated byproducts were first observed during the UV-C/NO3- photolysis, but only hydrogenated byproducts as adducts were detected during the UV-C/NO3-/CO32-/HCO3- photolysis. Nitrogenated and hydrogenated byproducts were formed in the early stage of degradation by OH or NO2 radicals, and these byproducts were subsequently degraded into smaller compounds with further reaction during UV-C/NO3- and UV-C/NO3-/CO32-/HCO3- reactions. In contrast, BPA was directly degraded into smaller compounds by ß-scission of the isopropyl group by CO3-/HCO3 radicals during UV-C/CO32-/HCO3- reaction. Our results imply that the water components can change the degradation mechanism of BPA during UV photolysis.

Persulfate enhanced photocatalytic degradation of bisphenol A by g-C3N4 nanosheets under visible light irradiation.

The enhancement of g-C3N4 photocatalytic degradation of bisphenol A (BPA) via persulfate (PS) addition was investigated under visible light irradiation. The effects of various parameters on the BPA degradation were investigated, such as catalysts dosage, PS concentrations, initial pH value and BPA concentration. The results showed that g-C3N4 nanosheets exhibited superior photocatalytic activity toward BPA degradation as compared with bulk g-C3N4. The addition of PS can further improve the g-C3N4 photocatalytic performance for BPA degradation. With 5 mM PS, the degradation rate of BPA was increased from 72.5% to 100% at 90 min, and the corresponding first-order kinetic constants were increased from 0.0028 to 0.0140 min-1. The removal efficiency of BPA increased with the decrease of solution pH value. The active radicals in the reaction system were tested by electron spin resonance (ESR) and radicals quenching experiments. Instead of persulfate radicals' oxidation, it was proposed that the main active radicals for BPA degradation were superoxide radicals and the photogenerated holes.

One stone two birds: novel carbon nanotube/Bi4VO8Cl photocatalyst for simultaneous organic pollutants degradation and Cr(VI) reduction.

In this work, visible light-responsive carbon nanotubes (CNTs)/Bi4VO8Cl composite photocatalysts have been prepared by a facile in situ hydrothermal method and characterized by various techniques. The photocatalytic properties of the photocatalysts are evaluated by the degradation of refractory azo-dye methyl orange (MO), hexavalent chromium Cr(VI), and bisphenol A (BPA) in water under visible light irradiation. It is found that the as-prepared composite with 4 wt% CNTs shows an optimal photocatalytic performance, and its photocatalytic activity is 30% higher than that of pure Bi4VO8Cl. The enhanced photocatalytic activity is ascribed to the synergetic effects induced by increased light absorption, increased adsorption efficiency for pollutant, and suppressed recombination rate of photogenerated charge carriers. Furthermore, efficient removals of Cr(VI), bisphenol A (BPA), and combined contamination of Cr(VI) and BPA over CNTs/Bi4VO8Cl composite further confirm that the degradation of organic pollutants is a photocatalytic mechanism rather than photosensitization of dye. Of particular importance is that removal efficiency of single pollutant can be promoted by the coexistence of the Cr(VI) and organics. The mechanism of synergetic promotion is discussed and attributed to the accelerated separation of charge carriers resulted from their simultaneously being captured by pollutants. Moreover, the CNTs/Bi4VO8Cl composite exhibits good stability and recycling performance in the photocatalytic degradation process. Therefore, the composite photocatalysts developed in the present work are expected to have the potential in purification of complex wastewater. Graphical abstract The separation of photogenerated charge carriers and adsorbing capacity as well as visible light absorption ability of Bi4VO8Cl are significantly promoted by coupling with carbon nanotubes. Simultaneous removal of Cr(VI) and organic pollutants can be achieved by CNTs/Bi4VO8Cl composite photocatalysts under visible light irradiation.

Heterogeneous UV/Fenton degradation of bisphenol A catalyzed by synergistic effects of FeCo2O4/TiO2/GO.

A new method for bisphenol A (BPA) degradation in aqueous solution was developed. The characteristics of BPA degradation in a heterogeneous ultraviolet (UV)/Fenton reaction catalyzed by FeCo2O4/TiO2/graphite oxide (GO) were studied. The properties of the synthesized catalysts were characterized using scanning electron microscopy, X-ray diffraction, and vibrating sample magnetometry. FeCo2O4 and TiO2 were grown as spherical shape, rough surface, and relatively uniform on the surface of GO (FeCo2O4/TiO2/GO). Batch tests were conducted to evaluate the effects of the initial pH, FeCo2O4/TiO2/GO dosage, and H2O2 concentration on BPA degradation. In a system with 0.5 g L-1 of FeCo2O4/TiO2/GO and 10 mmol L-1 of H2O2, approximately 90 % of BPA (20 mg L-1) was degraded within 240 min of UV irradiation at pH 6.0. The reused FeCo2O4/TiO2/GO catalyst retained its activity after three cycles, which indicates that it is stable and reusable. The heterogeneous UV/Fenton reaction catalyzed by FeCo2O4/TiO2/GO is a promising advanced oxidation technology for treating wastewater that contains BPA.

Genotoxicity assessment of membrane concentrates of landfill leachate treated with Fenton reagent and UV-Fenton reagent using human hepatoma cell line.

Membrane concentrates of landfill leachates contain organic and inorganic contaminants that could be highly toxic and carcinogenic. In this paper, the genotoxicity of membrane concentrates before and after Fenton and UV-Fenton reagent was assessed. The cytotoxicity and genotoxicity was determined by using the methods of methyltetrazolium (MTT), cytokinesis-block micronucleus (CBMN) and comet assay in human hepatoma cells. MTT assay showed a cytotoxicity of 75% after 24h of exposure to the highest tested concentration of untreated concentrates, and no cytotoxocity for UV-Fenton and Fenton treated concentrates. Both CBMN and comet assays showed increased levels of genotoxicity in cells exposed to untreated concentrates, compared to those occurred in cells exposed to UV-Fenton and Fenton reagent treated concentrates. There was no significant difference between negative control and UV-Fenton treated concentrates for micronucleus and comet assay parameters. UV-Fenton and Fenton treatment, especially the former, were effective methods for degradation of bisphenol A and nonylphenol in concentrates. These findings showed UV-Fenton and Fenton reaction were effective methods for treatment of such complex concentrates, UV-Fenton reagent provided toxicological safety of the treated effluent, and the genotoxicity assays were found to be feasible tools for assessment of toxicity risks of complex concentrates.

Degradation and mineralization of Bisphenol A (BPA) in aqueous solution using advanced oxidation processes: UV/H2O2 and UV/S2O8(2-) oxidation systems.

This work reports on the removal and mineralization of an endocrine disrupting chemical, Bisphenol A (BPA) at a concentration of 0.22 mM in aqueous solution using inorganic oxidants (hydrogen peroxide, H2O2 and sodium persulfate, Na2S2O8;S2O8(2-)) under UV irradiation at a wavelength of 254 nm and 40 W power (Io = 1.26 × 10(-6) E s(-1)) at its natural pH and a temperature of 29 ± 3 °C. With an optimum persulfate concentration of 1.26 mM, the UV/S2O8(2-) process resulted in ∼95% BPA removal after 240 min of irradiation. The optimum BPA removal was found to be ∼85% with a H2O2 concentration of 11.76 mM. At higher concentrations, either of the oxidants showed an adverse effect because of the quenching of the hydroxyl or sulfate radicals in the BPA solution. The sulfate-based oxidation process could be used over a wider initial pH range of 3-12, but the hydroxyl radical-based oxidation of BPA should be carried out in the acidic pH range only. The water matrix components (bicarbonate, chloride and humic acid) showed higher scavenging effect in hydroxyl radical-based oxidation than that in the sulfate radical-based oxidation of BPA. UV/S2O8(2-) oxidation system utilized less energy (307 kWh/m(3)) EE/O in comparison to UV/H2O2 system (509 kWh/m(3)) under optimum operating conditions. The cost of UV irradiation far outweighed the cost of the oxidants in the process. However, the total cost of treatment of persulfate-based system was much lower than that of H2O2-based oxidation system.

Bisphenol A release from orthodontic adhesives and its correlation with the degree of conversion.

INTRODUCTION: Our objective was to quantitatively assess and compare the bisphenol A (BPA) released from an orthodontic adhesive using a light-emitting diode device (LED) or a halogen light-curing unit (HLC) at 3 tip-to-bracket distances (0, 5, and 10 mm) and varying curing times using high-performance liquid chromatography. BPA release with self-etching and moisture-insensitive primers with light-cured and chemically cured composites was also evaluated. BPA release was correlated to the corresponding degree of conversion. METHODS: Our sample consisted of 598 stainless steel first premolar brackets. Of these, 520 were used for assessing BPA release and divided into 13 groups of 40 each. In groups I, II, and III, the composite was cured with the LED for 20 seconds at distances of 0, 5, and 10 mm, respectively. Groups IV, V, and VI were cured with the HLC for 40 seconds at the same 3 distances. Groups VII and VIII were cured for 5 and 10 seconds with the LED, and groups IX and X were cured for 10 and 20 seconds with the HLC at 0-mm distance. Groups XI, XII, and XIII consisted of brackets bonded with a self-etching primer and Transbond (3M Unitek, Monrovia, Calif), with a moisture-insensitive primer and Transbond, and with a chemically cured composite. The remaining 78 brackets were also divided into 13 groups and used for assessing the degree of conversion. RESULTS: The LED devices demonstrated significantly less BPA release and greater degrees of conversion (P <0.05). For both units, BPA release increased and the degree of conversion decreased as the tip distance increased and curing time decreased. The chemically cured group showed significantly less BPA release (P <0.05). Among the light-cured composites, those cured according to the manufacturers' recommendations (40 seconds and 0-mm distance for the HLC unit) released less BPA than did the self-etching primer and the moisture-insensitive primer. The degree of conversion was greatest for the chemically cured composite, whereas it was similar for the conventional, self-etching primer, and moisture-insensitive primer groups. However, correlations ranged from strongly negative to weakly positive between BPA release and degree of conversion. CONCLUSIONS: Clinicians should consider using LEDs in clinical practice and should keep the light-cure tip as close to the bracket as clinically possible. Curing time should be according to the manufacturer's recommendations. These steps will ensure less BPA release and a greater degree of conversion. Since chemically cured composites had less BPA release and a greater degree of conversion, they can be considered superior to light-cured composites in this aspect.

S2O8(2-)/UV-C and H2O2/UV-C treatment of Bisphenol A: assessment of toxicity, estrogenic activity, degradation products and results in real water.

The performance of S2O8(2-)/UV-C and H2O2/UV-C treatments was investigated for the degradation and detoxification of Bisphenol A (BPA). The acute toxicity of BPA and its degradation products was examined with the Vibrio fischeri bioassay, whereas changes in estrogenic activity were followed with the Yeast Estrogen Screen (YES) assay. LC and LC-MS/MS analyses were conducted to determine degradation products evolving during photochemical treatment. In addition, BPA-spiked real freshwater samples were also subjected to S2O8(2-)/UV-C and H2O2/UV-C treatment to study the effect of a real water matrix on BPA removal and detoxification rates. BPA removal in pure water was very fast (⩽7 min) and complete via both H2O2/UV-C and S2O8(2-)/UV-C treatment, accompanied with rapid and significant mineralization rates ranging between 70% and 85%. V.fischeri bioassay results indicated that degradation products being more toxic than BPA were formed at the initial stages of H2O2/UV-C whereas a rapid and steady reduction in toxicity was observed during S2O8(2-)/UV-C treatment in pure water. UV-C treatment products exhibited a higher estrogenic activity than the original BPA solution while the estrogenicity of BPA was completely removed during H2O2/UV-C and S2O8(2-)/UV-C treatments parallel to its degradation. 3-methylbenzoic and 4-sulfobenzoic acids, as well as the ring opening products fumaric, succinic and oxalic acids could be identified as degradation products. BPA degradation required extended treatment periods (>20 min) and TOC removals were considerably retarded (by 40%) in the raw freshwater matrix most probably due to its natural organic matter content (TOC=5.1 mg L(-1)). H2O2/UV-C and S2O8(2-)/UV-C treatment in raw freshwater did not result in toxic degradation products.

Arsenite oxidation-enhanced photocatalytic degradation of phenolic pollutants on platinized TiO2.

The effect of As(III) on the photocatalytic degradation of phenolic pollutants such as 4-chlorophenol (4-CP) and bisphenol A (BPA) in a suspension of platinized TiO2 (Pt/TiO2) was investigated. In the presence of As(III), the photocatalytic degradation of 4-CP and BPA was significantly enhanced, and the simultaneous oxidation of As(III) to As(V) was also achieved. This positive effect of As(III) on the degradation of phenolic pollutants is attributed to the adsorption of As(V) (generated from As(III) oxidation) on the surface of Pt/TiO2, which facilitates the production of free OH radicals ((•)OHf) that are more reactive than surface-bound OH radicals ((•)OHs) toward phenolic pollutants. The generation of (•)OHf was indirectly verified by using coumarin as an OH radical trapper and comparing the yields of coumarin--OH adduct (i.e., 7-hydroxycoumarin) formed in the absence and presence of As(V). In repeated cycles of 4-CP degradation, the degradation efficiency of 4-CP gradually decreased in the absence of As(III), whereas it was mostly maintained in the presence of As(III), which was either initially present or repeatedly injected at the beginning of each cycle. The positive effect of As(III) on 4-CP degradation was observed over a wide range of As(III) concentrations (up to mM levels) with Pt/TiO2. However, a high concentration of As(III) (hundreds of µM) inhibited the degradation of 4-CP with bare TiO2. Therefore, Pt/TiO2 can be proposed as a practical photocatalyst for the simultaneous oxidation of phenolic pollutants and As(III) in industrial wastewaters.

Cu-TiO2 nanorods with enhanced ultraviolet- and visible-light photoactivity for bisphenol A degradation.

In this study, the microwave-assisted sol-gel method and chemical reduction were used to synthesize Cu-TiO2 nanorod composites for enhanced photocatalytic degradation of bisphenol A (BPA) in the presence of UV and visible lights. The electron microscopic images showed that the Cu nanoparticles at 4.5±0.1nm were well-deposited onto the surface of TiO2 nanorods after chemical reduction of Cu ions by NaBH4. The X-ray diffractometry patterns and X-ray photoelectron spectroscopic results indicated that Cu species on the Cu-TiO2 nanorods were mainly the mixture of Cu2O and Cu(0). The Cu-TiO2 nanorods showed excellent photocatalytic activity toward BPA photodegradation under the irradiation of UV and visible lights. The pseudo-first-order rate constant (kobs) for BPA photodegradation by 7wt% Cu-TiO2 nanorods were 18.4 and 3.8 times higher than those of as-synthesized TiO2 nanorods and Degussa P25 TiO2, respectively, under the UV light irradiation. In addition, the kobs for BPA photodegradation by 7wt% Cu-TiO2 nanorods increased by a factor of 5.8 when compared with that of Degussa P25 TiO2 under the irradiation of 460±40nm visible light. Results obtained in this study clearly demonstrate the feasibility of using one-dimensional Cu-TiO2 nanorods for photocatalytic degradation of BPA and other pharmaceutical and personal care products in water and wastewater treatment plants.

A role for calcium hydroxide and dolomite in water: acceleration of the reaction under ultraviolet light.

Organic environmental pollutants are now being detected with remarkably high frequency in the aquatic environment. Photodegradation by ultraviolet light is sometimes used as a method for removing organic chemicals from water; however, this method is relatively inefficient because of the low degradation rates involved, and more efficient methods are under development. Here we show that the removal of various organic pollutants can be assisted by calcined dolomite in aqueous solution under irradiation with ultraviolet light. It was possible to achieve substantial removal of bisphenol A, chlorophenols, alkylphenols, 1-naphthol and 17ß-estradiol. The major component of dolomite responsible for the removal was calcium hydroxide. Our results demonstrate that the use of calcium hydroxide with ultraviolet light irradiation can be a very effective method of rapidly removing organic environmental pollutants from water. This is a new role for calcium hydroxide and dolomite in water treatment.

Multi adducts of diphenylmethanofullerenes as electron acceptors for polymer solar cells: a quantum chemical study.

In the present study, quantum chemical methods were applied to investigate the energy levels of the frontier orbital of mono and multi adducts of diphenylmethanofullerenes (DPMs). Recently these molecules have been used as electron acceptors in polymer solar cells showing interesting properties compared to the widely used [6, 6]-phenyl-C61-butyric acid methyl ester (PCBM). The geometries of all the investigated compounds were optimized with the density functional theory at the B3LYP/3-21G level of calculation. We studied the effect of electron-donating (methoxy and methyl thioether) and electron-withdrawing (fluorine) substituents (placed on the diphenylmethano addend in ortho, meta and para position of the phenyl rings), on the lowest unoccupied molecular orbital (LUMO) level of DPM. Afterward, we analysed all the possible isomers arising from bis and tris additions to fullerene cage. The LUMO level is significantly raised compared to the mono adduct but different isomers have different LUMO levels. Since the open circuit voltage (V(oc)) for polymer solar cells with ohmic contacts is proportional to the difference between the highest occupied molecular orbital (HOMO) of the donor polymer and the LUMO of the acceptor (fullerene), these bisadducts have the potential to increase the V(oc) of the corresponding devices.

Mesopolymer modified with palladium phthalocyaninesulfonate as a versatile photocatalyst for phenol and bisphenol A degradation under visible light irradiation.

A novel versatile photocatalyst, FDU-PdPcS, was prepared by immobilizing palladium phthalocyaninesulfonate (PdPcS) onto the FDU-15 mesopolymer via multi-step chemical modification processes involving chloromethylation of the FDU-15 mesopolymer first with chloromethyl methyl ether, a subsequent amination reaction with ethylenediamine, and finally modification with palladium phthalocyaninesulfonate via ionic interaction. The obtained FDU-PdPcS photocatalyst was characterized by the X-ray diffraction (XRD), UV-Vis spectrosopy and inductively coupled plasma (ICP) techniques. This photocatalyst not only affords a high dispersion of monomeric PdPcS molecules, which may further be stabilized by the pi-electron of benzene rings of FDU-15, but also provides a number of diamino groups inside the mesopores, which could be advantageous for the photodegradation of phenolic pollutants. In photodegradation studies of phenolic pollutants, the FDU-PdPcS catalyst exhibited excellent visible light photocatalytic activity and reusability. The photodegradation products of phenol and bisphenol A were investigated by the gas chromatoghraphy-mass spectrometry (GC-MS) technique. The results showed that the photodegradation products were composed of carboxylic acids and CO2. Isopropanol, sodium azide and benzoquinone were used as hydroxyl radical (OH*), singlet oxygen (1O2) and superoxide radical (O2*-) scavengers, respectively. The results suggested that 1O2 and O2*- were the prominent active species during the photodegradation process. A possible mechanism for the photodegradation of phenol was also discussed.

Visible-light-induced photocatalytic reduction of Cr(VI) with coupled Bi2O3/TiO2 photocatalyst and the synergistic bisphenol A oxidation.

Coupled Bi2O3/TiO2 photocatalysts were fabricated by sol-gel and hydrothermal methods and characterized using various spectroscopy techniques. Photocatalytic reduction of Cr(VI) in aqueous solution, together with the synergistic effect of photodegradation of bisphenol A (BPA), was investigated using these coupled Bi2O3/TiO2 under visible-light irradiation. Coupling of Bi2O3 inhibited the phase transformation from anatase to rutile and extended absorption region to visible light. Bi ions did not enter TiO2 lattice and were more likely to bond with oxygen atoms to form Bi2O3 on the surface of TiO2. Photovoltage signals in visible range revealed the effective interfacial charge transfer between Bi2O3 and TiO2. Two percent Bi2O3/TiO2 exhibited the highest photocatalytic activity of visible-light-induced reduction of Cr(VI). The addition of BPA effectively increased the photocatalytic reduction of Cr(VI). Simultaneously, the presence of Cr(VI) promoted the degradation of BPA, which was demonstrated by the investigation of TOC removal yield and generated intermediates. A possible mechanism of photocatalytic reduction of Cr(VI) and degradation of BPA in Bi2O3/TiO2 system was proposed. The synergistic effect, observed between reduction of Cr(VI) and degradation of BPA, provides beneficial method for environmental remediation and purification of the complex wastewater.

Environmentally friendly chemical recycling of poly(bisphenol-A carbonate) through phase transfer-catalysed alkaline hydrolysis under microwave irradiation.

The various and widespread uses of polycarbonate (PC) polymers require a meaningful and environmentally friendly disposal method. In this study, depolymerisation of polycarbonate with water in a microwave reactor is suggested as a recycling method. Hydrolysis was investigated in an alkaline (NaOH) solution using a phase-transfer catalyst. All of the experiments were carried out in a sealed microwave reactor, in which the reaction pressure, temperature and microwave power were continuously controlled and recorded. In the hydrolysis products, bisphenol-A monomer was obtained and identified by FTIR measurements. PC degradation higher than 80% can be obtained at 160°C after a microwave irradiation time of either 40 min or 10 min using either a 5 or 10% (w/v) NaOH solution, respectively. GPC, TGA and DSC measurements of the PC residues revealed that surface erosion is the degradation mechanism. First-order reaction kinetics were estimated by implementing a simple kinetic model. Finally, greater than 85% degradation was achieved when waste CDs were treated with the same method. The results confirm the importance of the microwave power technique as a promising recycling method for PC-based waste plastics, resulting in monomer recovery in addition to substantial energy savings.

One-pot solvothermal synthesis of three-dimensional (3D) BiOI/BiOCl composites with enhanced visible-light photocatalytic activities for the degradation of bisphenol-A.

Three-dimensional (3D) BiOI/BiOCl composite microspheres with enhanced visible-light photodegradation activity of bisphenol-A (BPA) are synthesized by a simple, one-pot, template-free, solvothermal method using BiI(3) and BiCl(3) as precursors. These 3D hierarchical microspheres with heterojunction structures are composed of 2D nanosheets and have composition-dependent absorption properties in the ultraviolet and visible light regions. The photocatalytic oxidation of BPA over BiOI/BiOCl composites followed pseudo first-order kinetics according to the Langmuir-Hinshelwood model. The highest photodegradation efficiency of BPA, i.e., nearly 100%, was observed with the BiOI/BiOCl composite (containing 90% BiOI) using a catalyst dosage of 1 g L(-1) in the BPA solution (C(0)=20 mg L(-1), pH=7.0) under visible light irradiation for 60 min. Under these conditions, the reaction rate constant was more than 4 and 20 times greater than that of pure BiOI and the commercially available Degussa P25, respectively. The superior photocatalytic activity of this composite catalyst is attributed to the suitable band gap energies and the low recombination rate of the photogenerated electron-hole pairs due to the presence of BiOI/BiOCl heterostructures. Only one intermediate at m/z 151 was observed in the photodegradation process of BPA by liquid chromatography combined with mass spectrometry (LC-MS) analysis, and a simple and hole-predominated photodegradation pathway of BPA was subsequently proposed. Furthermore, this photocatalyst exhibited a high mineralization ratio, high stability and easy separation for recycling use, suggesting that it is a promising photocatalyst for the removal of BPA pollutants.