OH Generation Ability Research Articles

Electrochemical reclamation of oil sands process water: Two and three-dimensional electrode configuration systems structured with different anode materials

Several studies have indicated the potential of the electrochemical advanced oxidation process in oil sands process water (OSPW) reclamation; however, the variations in different electrode configuration systems and anode materials remain elusive. This study assembled a two-dimensional electrode system (2-DES) and a packed bed electrode reactor (PBER) for OSPW reclamation, of which boron-doped diamond (BDD) (non-active anode), dimensionally stable anodes (DSA-RuO2 and DSA-IrO2) and graphite (active anodes) were selected as the anode materials, while in PBER, spherical activated carbon (SAC) was added as the third electrode. Within the 2-DES, BDD achieved over 60% removal of chemical oxygen demand (COD) due to its excellent •OH generation ability, while DSAs generated the most active chlorine and were quickly consumed by organic matter during the first 30 minutes. However, mass transfer limitation restricted the 2-DES treatment efficiency regardless of the anode materials employed, particularly resulting in limited removal of naphthenic acids (NAs). Compared to 2-DES, PBER significantly improved the OSPW treatment under identical electrolysis conditions, achieving over 91% COD and 99% NAs removal using DSA-IrO2 + SAC. Because of the contribution of the third electrode in PBER, the performance differences between various anode materials were less substantial than in the case of 2-DES. Packed SAC enhanced the mass transfer performance and generation of radical oxidants during OSPW electrolysis, improving the OSPW electrochemical treatment process. Additionally, SAC adsorbed most free chlorine from the liquid phase, avoiding the formation of halogenated organic compounds in reclaimed OSPW.

Electric field-enhanced heterogeneous catalytic ozonation (EHCO) process for sulfadiazine removal: The role of cathodic reduction

In this work, an electric field-enhanced heterogeneous catalytic ozonation (EHCO) was systematically investigated using a prepared FeOx/PAC catalyst. The EHCO process exhibited high sulfadiazine (SDZ) and TOC removal efficiency compared with electrocatalysis (EC) and heterogeneous catalytic ozonation (HCO) process. Almost 100% of SDZ was removed within 2 min, and the TOC removal reached approximately 85% within 60 min. Quenching experiments and EPR analysis suggested that the prominent SDZ and TOC removal performance is supported by the enhanced ·OH generation ability. Further study proved that H2O2 formed by O2 electrochemical reduction, peroxone reaction and electrochemical reduction of ozone contributed to improving ·OH generation. Furthermore, the EHCO system showed satisfactory stability and recyclability compared to conventional HCO systems, and the SDZ and TOC removal rates were maintained at ≥95% and ≥70% in 16 consecutive recycles, respectively. Meanwhile, XPS analysis and Boehm's titration for the FeOx/PAC catalyst used in HCO and EHCO process confirmed that the external electron supply could restrain the oxidation of surface functional groups of PAC and maintain a balance of the Fe(II)/Fe(III) ratio, which proved the critical role of cathode reduction in catalyst in situ regeneration during long consecutive recycles. In addition, the EHCO system could achieve more than 80% SDZ removal within 2 min in different water matrices. These results confirmed that the EHCO process has a wide application perspective for refractory organics removal in actual wastewater.

Electrochemical oxidation of carbamazepine in water using enhanced blue TiO2 nanotube arrays anode on porous titanium substrate

In this study, a blue TiO2 nanotube arrays anode on porous titanium substrate (Ti-porous/blue TiO2 NTA) was successfully fabricated by facile anodization and in situ reduction, and was used to investigate the electrochemical oxidation of carbamazepine (CBZ) in aqueous solution. The surface morphology and crystalline phase of the fabricated anode were characterized by SEM, XRD, Raman spectroscopy and XPS, and the electrochemical analysis confirmed that blue TiO2 NTA on Ti-porous substrate had larger electroactive surface area, better electrochemical performance and higher ⋅OH generation ability than that on Ti-plate substrate. The removal efficiency of 20 mg L−1 CBZ in 0.05 M Na2SO4 solution reached 99.75% at 8 mA cm−2 after 60 min electrochemical oxidation, and the rate constant was 0.101 min−1 with low energy consumption. EPR analysis and free radical sacrificing experiments showed that ⋅OH played a key role in the electrochemical oxidation. The possible oxidation pathways of CBZ were proposed through the identification of degradation products, and the main reactions may involve deamidization, oxidization, hydroxylation and ring-opening. Compared with Ti-plate/blue TiO2 NTA anode, Ti-porous/blue TiO2 NTA anode displayed excellent stability and reusability, and is promising to be used in the electrochemical oxidation of CBZ in wastewater.

Novel Sb-SnO2 Electrode with Ti3+ Self-Doped Urchin-Like Rutile TiO2 Nanoclusters as the Interlayer for the Effective Degradation of Dye Pollutants.

Stable and efficient SnO2 electrodes are very promising for effectively degrading refractory organic pollutants in wastewater treatment. In this regard, we firstly prepared Ti3+ self-doped urchin-like rutile TiO2 nanoclusters (TiO2-x NCs) on a Ti mesh substrate by hydrothermal and electroreduction to serve as an interlayer for the deposition of Sb-SnO2 . The TiO2-x NCs/Sb-SnO2 anode exhibited a high oxygen evolution potential (2.63 V vs. SCE) and strong ⋅OH generation ability for the enhanced amount of absorbed oxygen species. Thus, the degradation results demonstrated its good rhodamine B (RhB), methylene blue (MB), alizarin yellow R (AYR), and methyl orange (MO) removal performance, with the rate constant increased 5.0, 1.9, 1.9, and 4.7 times, respectively, compared to the control Sb-SnO2 electrode. RhB and AYR degradation mechanisms are also proposed based on the results of high-performance liquid chromatography coupled with mass spectrometry and quenching experiments. More importantly, this unique rutile interlayer prolonged the anode lifetime sixfold, given its good lattice match with SnO2 and the three-dimensional concave-convex structure. Consequently, this work paves a new way for designing the crystal form and structure of the interlayers to obtain efficient and stable SnO2 electrodes for addressing dye wastewater problems.

Fabrication of a novel Ti3C2-modified Sb-SnO2 porous electrode for electrochemical oxidation of organic pollutants

Sb-SnO2 is an appealing electrode for degrading organic pollutants in wastewater treatment, albeit further modifications are needed for its inefficient electrochemical oxidation capacity. In this work, we prepared Ti3C2-modified Sb-SnO2 electrode by electrodeposition technology. High-conductive MXene matrix regulated the Sb-Sn alloy nucleation process to decrease its domain size during deposition and generated pores during the annealing process. When introducing 20 mg MXene into the electrolyte, the obtained Sb-SnO2 electrode (Ti3C2-20) presented a larger oxygen evolution over-potential (2.32 V vsSCE), increased amount of active sites, and enlarged electrochemical specific surface area (∼4.4-fold) than the unmodified electrode, resulting in a promoted OH generation ability (∼7.4 times). Methylene blue (MB), methyl orange (MO), norfloxacin (NOR), and P-phenylenediamine (PPD) were effectively degraded by the Ti3C2-20 anode with economic energy consumption. Moreover, the Ti3C2-20 electrode also featured a longer lifetime, almost fivefold, than the unmodified Sb-SnO2 electrode due to its larger loading amount and decreased charge transfer resistance. Consequently, this work offers a new perspective for designing efficient and stable porous electrodes to address water pollution issues.

Preparation of a novel Ce and Sb co-doped SnO2 nanoflowers electrode by a two-step (hydrothermal and thermal decomposition) method for organic pollutants electrochemical degradation

Nanostructured Sb-SnO2 electrodes with high electrochemical activity and stability are urgently desired for electrochemical oxidation of refractory organics in wastewater treatment, yet hard to be controlled and synthesized. Hence, we combined the hydrothermal method and thermal decomposition technologies to prepare a novel Ce and Sb co-doped SnO2 nanoflowers electrode (Ti/Ce-Sb-SnO2NFs). The incorporation of Ce endowed the Ti/Ce-Sb-SnO2NFs anode with an increased oxygen evolution over-potential (OEP) (1.99 V vs.SCE), lower charge transfer resistance (7.54 Ω⋅cm2), large specific electrochemical active surface area (141.83), a great number of active sites and superior •OH generation ability. Consequently, nearly 100% decolorization efficiency and 91.45% chemical oxygen demand (COD) mineralization efficiency of methylene blue (MB) (20 mg/L) were achieved by the Ti/Ce-Sb-SnO2NFs anode within 90 min. Additionally, the Ti/Ce-Sb-SnO2NFs anode stability was also improved with a longer accelerated lifetime (15.5 h) than the given Ti/Sb-SnO2NFs electrode (8.2 h). We also prepared other nanostructured (nanoparticles, nanoclusters and nanosheets) Sb-SnO2 electrodes with high oxidation capacity utilizing this two-step method, which demonstrated its great versatility. Accordingly, this work could provide a new strategy for fabricating efficient and stable rare earth elements (Ce, Nd, La, etc.) and Sb co-doped SnO2 nanostructured electrodes for decomposition organic pollutants in the field of wastewater treatment.

Fabrication of a Ti/PbO2 electrode with Sb doped SnO2 nanoflowers as the middle layer for the degradation of methylene blue, norfloxacin and p-dihydroxybenzene

In the preparation of Sb-SnO2 internal layer of PbO2 electrode, the traditional thermal decomposition method has many problems, such as environmental pollution, short service life and low catalytic activity. Herein, a three-dimensional (3D) Sb doped SnO2 nanoflowers interlayer with good conductivity was prepared on the titanium substrate by the hydrothermal strategy to fabricate a novel PbO2 electrode (Ti/Sb-SnO2NFs/PbO2). Compared to the traditional PbO2 anode, a more compact and undulating 3D morphology of Ti/Sb-SnO2NFs/PbO2 electrode exhibited a higher total and inner active sites and stronger ·OH generation ability. Specifically, three typical organics, methylene blue (MB), norfloxacin (NOR) and p-dihydroxybenzene (p-DHB), were effectively degraded by the novel Ti/Sb-SnO2NFs/PbO2 electrode with economic energy consumption and the degradation mechanism of MB was also investigated. This 3D interlayer also improved the anode stability and safety with the lifetime prolonged about 2.70 times (from 30.1 h to 81.3 h). Consequently, this work offers a meaningful method to prepare PbO2 anode with high catalytic activity and good stability for wastewater treatment.

Preparation and characterization of Nd-Sb co-doped SnO2 nanoflower electrode by hydrothermal method for the degradation of norfloxacin

• Nd-Sb co-doped SnO 2 nanoflower electrode was prepared by hydrothermal method. • Proper amount of Nd doping could improve the electrocatalytic performance and stability of the SnO 2 electrode. • Three degradation pathways of norfloxacin were proposed. The unsatisfactory electrochemical activity and short service lifetime limited the wide application of Sb-doped SnO 2 electrode. Here, Nd-Sb co-doped SnO 2 nanoflower electrode on the Ti substrate was prepared by hydrothermal method. When the molar ratio of Nd:Sn was 7.5% in the precursor solution, the electrode has a small crystal size, large specific surface area, high oxygen evolution over-potential (2.18 V vs. SCE), low charge transfer resistance and strong ·OH generation ability. Hence, the Nd 7.5% electrode exhibited an excellent electrocatalytic activity with high chemical oxygen demand (COD) and total organic carbon (TOC) removal efficiency, and economic current efficiency for the degradation of norfloxacin (NOR). The effects of Nd doping content, Na 2 SO 4 concentration, temperature, initial solution pH, initial NOR concentration and inorganic ions were also investigated. The degradation mechanism was explored by HPLC-MS and three degradation pathways were proposed. The toxicity of NOR and its intermediate products were evaluated by E. coli bacteria. Compared with Nd 0%, the lifetime of Nd 7.5% also prolonged about 3.5 times for the anti-corrosion ability of Nd. Thus, the Nd-Sb co-doped SnO 2 nanoflower electrode with good electrooxidation activity and high stability provides a new strategy for the degradation of norfloxacin by electrochemical oxidation technology.

Pollutants from primary sources dominate the oxidative potential of water-soluble PM2.5 in Hong Kong in terms of dithiothreitol (DTT) consumption and hydroxyl radical production

Increasing scientific findings show that the adverse health effects of PM2.5 are related not only to its mass but also PM2.5 sources and chemical compositions. Here, we conducted a comprehensive characterization and source apportionment of oxidative potential (OP) of water-soluble PM2.5 collected in Hong Kong for one year. Two OP indicators, namely dithiothreitol (DTT) consumption and ∙OH formation, were quantified. Six PM2.5 sources, i.e. secondary sulfate, biomass burning, secondary organic aerosol (SOA), vehicle emissions, marine vessels, and a metal-related factor, were apportioned and identified to be DTT active. The four primary sources accounted for 83.5% of DTT activity of water-soluble PM2.5, with the metal-related factor and marine vessels as the leading contributors. However, only three sources, i.e. metal-related factor, vehicle emissions, and SOA, showed ∙OH generation ability, with a predominant contribution of 96.2% from the two primary sources, especially the metal-related factor (84.5%). Based on the source apportionment results, we further evaluate the intrinsic OP of water-soluble PM2.5 from each source. Marine vessels exhibited the highest intrinsic DTT activity; while metal-related factor was most effective in ∙OH generation.

Synthesis of CQDs@FeOOH nanoneedles with abundant active edges for efficient electro-catalytic degradation of levofloxacin: Degradation mechanism and toxicity assessment

The occurrence of antibiotics in water environment has drawn great concerns in recent years. In this work, CQDs@FeOOH electro-catalyst with abundant active edges was synthesized and applied to the degradation of antibiotics. About 99.6 % levofloxacin (LEVO) and 53.7 % TOC could be efficiently removed by CQDs@FeOOH after 60 min degradation. The high LEVO degradation performance of CQDs@FeOOH was demonstrated to be attributed to the high mass transfer ability and the high OH generation ability of the special needles structure. The OH was found to be the main radical for LEVO degradation, and the highest OH generation ability of CQDs@FeOOH was found to be resulted from the moderate adsorption energy of the exposed (1 1 0) facets (needles) toward OH. A possible LEVO degradation pathway has been proposed and toxicity changes during LEVO degradation were detailed investigated. This study offers an efficient method to reduce the amount and toxicity of antibiotics in water.

A novel Pb/PbO2 electrodes prepared by the method of thermal oxidation-electrochemical oxidation: Characteristic and electrocatalytic oxidation performance

The PbO2 electrodes were preservative and chemically stable but had the problem of the poor electrocatalytic oxidation activity and instability. In this research, Pb/PbO2 electrodes with good electrocatalytic oxidation activity and stability were prepared via a novel combined method of thermal oxidation and electrochemical oxidation, which was different form electrodeposition and coating method. Combined with the results analyzed by SEM, metallographic microscope, XRD, steady-state polarization and CV tests, the electrocatalytic oxidation performance was evaluated by the generation capacity of ·OH and the removal efficiency of Congo red (CR). The experimental results put in evidence that the electrochemical oxidation time affected the electrochemical oxidation performance of Pb/PbO2 electrode by refinement of crystal sizes and strengthening of crystallinity which promoted oxygen evolution potential and ·OH generation ability. The better ·OH generation ability of 6-PbO2 encouraged the removal of CR (68.62%, 0.177 min−1) whose chromophore and ring structure of aromatic hydrocarbons was destroyed by ·OH (7.82 × 10−4 μM min−1) with initial concentration of 20 mg·L-1 at 8 mA·cm-2 for 20 min. Moreover, 6-PbO2 owned stability for its compact surface. It showed that the stable 6-PbO2 electrode prepared by the thermal oxidation-electrochemical oxidation method had good electrocatalytic oxidation activity and excellent application potential, which were worthy of further research.

Synthesizing ZnWO4 with enhanced performance in photoelectrocatalytic inactivating marine microorganisms

ZnWO4 was synthesized by a hydrothermal method, and different molar ratios of Zn2+/WO42− were prepared in precursor solution systems (Zn2+:WO42− = 1:1, 2:1, 3:1, 4:1, 1:2, 1:3, 1:4) in the synthesis process. On the whole, the photocatalytic activity increases with excess Zn2+ and decreases when excess WO42− is in the precursor solution; the sample exhibited the best performance when Zn2+:WO42− = 3:1, with inactivation time of 7 min, which is 36% shorter than for the original sample (1:1). The CV tests showed that the OH generation ability strengthened with excess Zn2+ and weakened with abundant WO42−; according to the SEM results, long and uniform nanorods can be gained when Zn2+ is in excess in the precursor solution, and the morphology became bulky in the case of WO42−. Apart from the morphology and properties, the immanent cause is the exposed (100) high energy plane under the Zn2+-rich condition. Generally, the molar ratio of Zn2+/WO42− in the precursor solution could adjust the morphology and face exposure of products and improve the photocatalytic activity of ZnWO4. Simultaneously, photoelectrocatalytic technology can effectively separate the e−/h+ pairs, which greatly enhances the inactivation activity.

Photocatalytic oxidation of MEK over hierarchical TiO2 catalysts: Effect of photocatalyst features and operating conditions

A novel hydrothermal route was developed to synthesize crystalline and hierarchically porous TiO2 at mild conditions under acidic/basic reaction environments. A good control over the key features of catalysts could be achieved by varying the pH of the starting solution (pH = 2–12) and type of acid during preparation. Crystalline, textural, and optical properties of photocatalysts were characterized in order to explore the connections between catalysts’ features and photoactivity. The activities of catalysts were evaluated for decomposition of methyl ethyl ketone (MEK) in a continuous flow photoreactor. To gain insight into the impact of main operating conditions on photocatalytic oxidation (PCO) processes, experiments were conducted at wide ranges of inlet concentration, relative humidity, and residence time. X-ray diffraction (XRD) and transmission electron microscopy (TEM) confirmed that yielded titania samples possess good crystallinity and mainly consist of anatase polymorph. Results of X-ray photoelectron spectroscopy (XPS) indicated that the population of hydroxyl groups on the surface of TiO2 declines as the acidity of hydrothermal solution increases. Hierarchical porous structure with ultra-long parallel macrochannels and large macropores (> 0.5 μm) could be directly observed in scanning electron microscopy (SEM). The multimodal porous structure offers higher light utilization, enhanced mass transport, and superior adsorption capacity for air pollutants. Photoluminescence spectroscopy revealed that the enhancement in crystallinity has an impact on the separation of photo-induced charge carriers. Moreover, a satisfactory linear correlation between the ability of photocatalysts to generate •OH and crystallinity could be found. Under the harshest operating condition (residence time = 0.012 s, relative humidity = 50%, concentration = 1000 ppb), the TiO2 synthesized in nitric acid (pH = 4) achieved the highest MEK removal efficiency, 36.9%, which substantially surpassed that of P25, 14.5%. Hierarchical porosity, optimum trade-off between surface area and crystallinity, existence of meso- and macropores, small crystal size, and high •OH generation ability could account for the superior performance. A tentative reaction pathway for MEK photodegradation and a health-risk index were put forward considering the by-products detected in the gas phase.

Fabrication of a hydrophobic SDBS-PbO2 anode for electrochemical degradation of nitrobenzene in aqueous solution

In present work, a hydrophobic PbO2 electrode modified by sodium dodecyl benzene sulfonate (SDBS-PbO2) was fabricated using electrodeposition method. The effect of SDBS concentration in electroplating bath on the surface morphology, structure, electrochemical properties, hydrophilicity, OH generation ability and stability of SDBS-PbO2 electrodes was studied using scanning electron microscopy (SEM), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), cyclic voltammetry (CV), water contact angle, fluorescence probe technique, and accelerated life test, respectively. Results showed that SDBS modification not only increased the electro-catalytic activity, but also prolonged the service life of PbO2 electrode. The electrode prepared from the electroplating bath containing 10 mg/L SDBS (SDBS-PbO2-10 mg/L) showed the highest electrocatalytic activity and the longest service life. The electrochemical degradation of nitrobenzene (NB) in simulated wastewater was used to evaluate the potential application of SDBS-PbO2 electrodes for wastewater treatment. The highest NB removal efficiency and total organic carbon (TOC) removal efficiency of 89.35% and 52.62% were both obtained by SDBS-PbO2-10 mg/L anode. Thus, the SDBS-PbO2-10 mg/L anode was used to systematically investigate the effects of applied current density, initial NB concentration, temperature, and pH value on the reaction kinetics and mineralization current efficiency (MCE) of NB degradation. It was found that the increase of applied current density and the reduction of initial NB concentration exerted a prominent effect on the degradation of NB, but caused the decrease of MCE, while high temperature and low pH value improved both NB degradation rate and MCE. These results show that the SDBS-PbO2-10 mg/L electrode may become a promising anode for organic pollutant degradation.

Preferential electrocatalytic degradation of 2,4-dichlorophenoxyacetic acid on molecular imprinted mesoporous SnO2 surface

A molecular-imprinted mesoporous SnO2 electrode surface has been developed to achieve deep degradation of 2,4-dichlorophenoxyacetic acid (2,4-D) in complex coexisting system. Preferential electrocatalytic degradation of 2,4-D on our prepared electrode was observed in both the single component and coexisting system. The concentration of 2,4-D dropped down to 54 ppb after 6 h degradation in the coexisting sewage water system. The result reveals that our prepared electrode exhibited specific electrochemical recognition of target molecular 2,4-D. Besides, the mesoporous structure of SnO2 was proved to be great improvement of electrochemical activity with higher BET surface area (∼148.8 m2 g−1), electrochemical effective surface area (7.41 cm2 cm−2) and ·OH generation ability (66.5 μmol L−1) compared to conventional SnO2 electrode. However, the electrochemical activity influenced by the construction of MI sites was negligible. Furthermore, the preferential adsorption of 2,4-D on the surface of MI-meso SnO2 electrode was proved by both FT-IR spectra and chronocoulometry method.

Efficient Photodegradation of Endocrine-Disrupting Chemicals with Bi2O3–ZnO Nanorods Under a Compact Fluorescent Lamp

Nanoscaled Bi2O3 particles coated on ZnO nanorods (ZNRs) have been fabricated by combining hydrothermal technique with a chemical precipitation method. X-ray diffraction, field emission-scanning electron microscopy, transmission electron microscopy, energy dispersive X-ray spectroscopy, Fourier transform infrared spectroscopy, and UV–vis absorption and photoluminescence studies were adapted to characterize the structure, morphologies, and optical properties of the nanocomposites. The results indicated that small Bi2O3 nanoparticles were well distributed on the surfaces of ZNRs. And the Bi2O3–ZNR nanocomposites showed high charge separation efficiency and •OH generation ability as evidenced by photoluminescence spectra. Under irradiation of a 55-W compact fluorescent lamp, the Bi2O3–ZNR nanocomposites demonstrated photocatalytic activities higher than pure ZNRs in the degradation of two endocrine-disrupting chemicals, phenol and methylparaben, which might be attributed to the high separation efficiency of photogenerated electron–hole pairs based on the cooperative role of Bi2O3 loading on ZNRs. Moreover, the Bi2O3–ZNR nanocomposite could be easily recovered and reused due to their one-dimensional nanostructural property. All these characteristics brought enormous benefits of Bi2O3–ZNR nanocomposites to the practical application in indoor environmental remediation.

Photocatalytic performance of novel samarium-doped spherical-like ZnO hierarchical nanostructures under visible light irradiation for 2,4-dichlorophenol degradation

A novel samarium-doped spherical-like ZnO hierarchical nanostructure (Sm/ZnO) was synthesized via a facile and surfactant-free chemical solution route. The as-synthesized products were characterized by X-ray diffraction, Brunauer–Emmett–Teller surface area analysis, field emission scanning electron microscopy together with an energy dispersion X-ray spectrum analysis, transmission electron microscopy, UV–visible diffuse reflectance spectroscopy, and photoluminescence spectroscopy. The results revealed that Sm ion was successfully doped into ZnO. It was also observed that the Sm doping increased the visible light absorption ability of Sm/ZnO and a red shift for Sm/ZnO appeared when compared to pure ZnO. The photocatalytic studies revealed that the Sm/ZnO exhibited excellent photocatalytic degradation of 2,4-dichlorophenol (2,4-DCP) compared with the pure ZnO and commercial TiO2 under visible light irradiation. The photocatalytic enhancement of Sm/ZnO products was attributed to their high charge separation efficiency and OH generation ability as evidenced by the photoluminescence spectra. The photocatalytic investigation also showed that various parameters exerted their individual influence on the degradation rate of 2,4-DCP. By using a certain of radical scavengers, OH was determined to play a pivotal role for the 2,4-DCP degradation. Moreover, the Sm/ZnO could be easily separated and reused, indicating great potential for practical applications in environmental cleanup.

Investigation on visible-light photocatalytic degradation of 2,4-dichlorophenoxyacetic acid in the presence of MoO3/ZnO nanorod composites

Nanoscaled MoO3 particles loaded on ZnO nanorods (ZnO NRs) were synthesized via a hydrothermal-precipitation method. X-ray diffraction, field emission-scanning electron microscopy, high resolution transmission electron microscopy, energy dispersive X-ray spectroscopy, Fourier transform infrared spectroscopy, UV–vis absorption and photoluminescence studies were used to characterize the structures, morphologies and optical properties of the composites. The results showed that pure orthorhombic phase of α-MoO3 nanoparticles with average sizes of 15–21nm were well dispersed on the surface of ZnO NRs. The MoO3/ZnO NR composites also showed high charge separation efficiency and ·OH generation ability as evidenced by their photoluminescence spectra. The photocatalytic studies revealed that the MoO3/ZnO NRs showed superior visible-light degradation rate for herbicide 2,4-dichlorophenoxyacetic acid (2,4-D) compared with the pure ZnO NRs. Such enhancement might be attributed to the high separation efficiency of photogenerated electron–hole pairs based on the cooperative roles between bi-components of MoO3 and ZnO NRs. The photocatalytic studies also showed that various parameters such as the MoO3 content in the composite, MoO3/ZnO NRs amount, initial 2,4-D concentration and solution pH exerted their individual influence on the 2,4-D degradation. Moreover, the MoO3/ZnO NRs could be easily recovered and reused due to their one-dimensional nanostructural property.

Preparation and photocatalytic properties of visible light-driven samarium-doped ZnO nanorods

Samarium-doped ZnO nanorods (Sm/ZNRs) were newly synthesized via a facile and surfactant-free solvothermal method. The as-synthesized products were characterized by X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM) together with an energy dispersion X-ray spectrum (EDX) analysis, transmission electron microscopy (TEM), high resolution transmission electron microscopy (HRTEM), UV–visible diffuse reflectance spectra (UV–vis DRS) and photoluminescence (PL) spectra. The XRD and EDX results revealed that Sm ion was successfully doped into ZNRs. It was also observed that the Sm doping increased the visible light absorption ability of Sm/ZNRs and a red shift for Sm/ZNRs appeared when compared to pure ZNRs. The photocatalytic activity of the products was evaluated by the photocatalytic degradation of phenol aqueous solution under visible light irradiation. The results showed that all the Sm/ZNRs exhibited higher photocatalytic activities than that of the pure ZNRs. Such enhancement was attributed to their high charge separation efficiency and OH generation ability as evidenced by the PL spectra. The photocatalytic studies also showed that various effects of parameter had remarkable effect on the degradation rate of phenol. In addition, the one-dimensional structure of Sm/ZNRs could be easily recycled and reused, showing great potential for practical applications in environmental cleanup.

Preparation and characterization of visible-light-driven N–F–Ta tri-doped TiO2 photocatalysts

A new strategy to synthesize visible-light-driven N doped and N–F–Ta tri-doped TiO2 nanocatalysts via a hydrothermal combined with heat treatment method applied in Rhodamine B (RhB) and phenol decomposition was reported. The tri-doped sample gave the highest visible-light photocatalytic activity when the molar ratio of Ta to Ti was 1%. At a low tri-doping level, physicochemical analysis indicated that the synergistic effects of N, F and Ta could effectively increase not only the crystallite surface area but also the light absorption and OH generation ability, which contributed to the enhancement of visible-light photocatalytic activities. EPR and XPS analysis demonstrated that N–Ta interaction induced the charge compensation to form N 2p–Ta 5d hybridized states which improved the separation ability of the photoexcited electron–hole pairs. Still, F incorporation facilitated the incorporation of N which further promoted the N 2p–Ta 5d hybridized states. The N 2p, π*N–O, oxygen vacancy, Ti3+ and Ta 5d states were also responsible for the band gap narrowing. However, a high tri-doping level would affect the crystal growth and introduce too many defects into the lattice, reducing the visible-light photoactivity.