Phenol Removal Rate Research Articles

Ultrasound-assisted electrochemical treatment for phenolic wastewater.

With the rapid development of industry, especially the rapid rise of the chemical industry, the problem of water pollution is becoming more and more serious. Among them, the discharge of organic pollutants represented by phenolic substances has always been at the forefront. In this paper, ultrasound-assisted electrochemical treatment for phenolic wastewater is investigated. The effects of ultrasonic frequency, current, pH value and the amount of fly ash-loaded titanium TiO2-Fe3+ particles on phenol removal from phenol-containing wastewater are investigated. The experimental results demonstrate that the removal rate of phenol in phenol-containing wastewater is the best when ultrasonic frequency is 45kHz, power is 200W, the current is 1.2 A, pH is 5 and the dosage of fly ash-loaded titanium TiO2-Fe3+ particles is 3g. In addition, microwave-assisted-Fenton reagent treatment for phenol wastewater is investigated. The effects of Fenton reagent dosage, initial pH value, microwave power density and radiation time on phenol degradation rate are investigated. The results show that microwave can accelerate the reaction rate, reduce the number of metal ions, save the process cost and reduce the difficulty of post-treatment. Finally, the research status of phenol wastewater treatment technology at the present stage is reviewed, and the future development direction is discussed.

Acid etching followed by hydrothermal preparation of nanosized Bi2O4/Bi2O3 p-n junction as highly efficient visible-light photocatalyst for organic pollutants removal

As a promising visible-light photocatalyst, Bi2O4 has the advantage of broadband spectral response range. However, the high recombination rate of photoexcited charge carriers induced by the submicrorod morphology of pure Bi2O4 greatly restricts its visible-light photocatalytic performance. Herein, a novel nanosized Bi2O4/Bi2O3 p-n junction was developed by a dilute HCl acid etching and subsequent hydrothermal method, using NaBiO3·2H2O as the sole bismuth precursor. A product of NaBiO3·2H2O@BiOCl was formed firstly when NaBiO3·2H2O was partially reduced by insufficient dilute HCl aqueous solution. Then, BiOCl reacted with NaBiO3·2H2O during the following hydrothermal reaction process, resulting in the formation of Bi2O4 nanoparticles (NPs) anchored on the surface of plate-like Bi2O3. The content of Bi2O3 in the junction can be easily controlled by changing the added amount of dilute HCl acid. This strategy could not only realize the NPs-sized Bi2O4 but also construct nanometered Bi2O4/Bi2O3 p-n junction simultaneously, which remarkably improves the separation efficiency of charge carriers. Furthermore, the obtained Bi2O4/Bi2O3 heterojunctions have larger specific surface areas than Bi2O4 alone. Due to these advantages, the photocatalytic removal rate of methyl orange (MO) and phenol for the optimal Bi2O4/Bi2O3 heterostructure increased respectively by 5.06 and 2.16 times under visible light, when compared with single Bi2O4. The results of active species trapping experiment and electron spin resonance (ESR) spectra indicate that holes (h+) and superoxide radicals (O2−) are the primary and secondary reactive active species during the photocatalytic degradation process, respectively. This work provides a novel perspective for the design and preparation of high performance Bi2O4-based photocatalyst.

Catalytic activity and evaluation of Fe-Mn@Bt for ozonizing coal chemical biochemical tail water

The purpose of this study was to improve the ozone utilization rate by preparing a high-efficiency ozone catalyst, and establish an effective model to evaluate catalytic oxidation systems. In this study, Fe-Mn@Bt ozone catalyst prepared by a doping-baking method was used to deeply treat the biochemical tail water of coal chemical wastewater. The catalyst had an extremely developed pore structure characterized by SEM. The catalytically active elements inside and on the catalyst in the form of α-Fe2O3 and MnO2 had good stability. The effects of operating conditions, such as ozone dosage, hydraulic retention time, and catalyst dosage, on total phenol and total organic carbon (TOC) removal rate were systematically investigated. Under optimal working conditions, the chemical oxygen demand (COD) after the degradation of coal chemical biochemical tail water was used as the evaluation index to explore the actual utilization rate of ozone. The addition of Fe-Mn@Bt porous catalyst upgraded the actual utilization rate of ozone from 0.14. kgCOD/kgO3 (ozone alone oxidation system) to 0.22 kg COD/kg O3. The mechanism of catalytic oxidation was investigated by adding a free radical inhibitor to a catalytic oxidation system, demonstrating that the dominant processes in a deep degradation system was that the catalysis of ozone-generated hydroxyl radicals by active elements and ozone oxidation. To further evaluate the operating conditions for Fe-Mn@Bt ozone catalyst, the “3E” evaluation system where economy, energy, and environment were the key factors was established and evaluated. At optimal levels, the removal ratios of total phenol and TOC were 58.7% and 53.5%, respectively. Fe-Mn@Bt ozone catalysts can effectively improve ozone utilization rate and has a good application prospect for the advanced treatment of coal chemical wastewater.

Influence of Oxygen Vacancy in Mangan-based Catalyst on Phenol Removal Via Catalytic Ozonation

In order to improve the performance of the catalyst applied in ozonation, this work show the hydrothermal synthesis routine to prepare MnO₂ with different oxygen vacancy content. The α-MnO₂ was aminated and further processed with doped graphene oxide (GO) to obtain high oxygen vacancy content α-MnO₂-NH₂-GO, which was subsequently used for catalyzing ozonation phenol degradate. The catalysts were characterized by X-ray diffraction (XRD), X-ray photoelectron spectra (XPS), Brunner-Emmet-Teller (BET), H₂-temperature-programmed reduction (H₂-TPR), scanning electron microscopy (SEM), etc. Characterization and experimental results showed that the oxygen vacancy content has an important effect on the catalytic performance of the catalyst, MnO₂ with low average oxidation state showed better catalytic ozonation performance. The coexistence of Mn³⁺ and Mn⁴⁺ have great significant role for the continuous generation of free radicals and the restoration of oxygen vacancies. The doping of GO can increase the electron transfer rate, and improve the catalytic performance. The catalytic performance of α-MnO₂-NH₂-GO is better than α-MnO₂, phenol removal rate can achieve more than 99% within 30 min, and superoxide radicals can be determined by different free radical trapping agents. The results of main active oxygen and reaction kinetics research showed that the degradation of phenol is a first-order reaction whether α-MnO₂-NH₂-GO or α-MnO₂ is used as a catalyst.

Engineered bacterial biofloc formation enhancing phenol removal and cell tolerance.

A microbial floc consisting of a community of microbes embedded in extracellular polymeric substances matrix can provide microbial resistances to toxic chemicals and harsh environments. Phenol is a toxic environmental pollutant and a typical lignin-derived phenolic inhibitor. In this study, we genetically engineered Escherichia coli cells by expressions of diguanylate cyclases (DGCs) to promote proteinaceous and aliphatic biofloc formation. Compared with the planktonic E. coli cells, the biofloc-forming cells improved phenol removal rate by up to 2.2-folds, due to their substantially improved tolerance (up to 149%) to phenol and slightly enhanced cellular activity (20%) of phenol hydroxylase (PheH). The engineered bioflocs also improved E. coli tolerance to other toxic compounds such as furfural, 5-hydroxymethylfurfural, and guaiacol. Additionally, the strategy of the engineered biofloc formation was applicable to Pseudomonas putida and enhanced its tolerance to phenol. This study highlights a strategy to form engineered bioflocs for improved cell tolerance and removal of toxic compounds, enabling their universality of use in bioproduction and bioremediation.

Dielectric barrier discharge-coupled Fe-based zeolite to remove ammonia nitrogen and phenol pollutants from water

In this work, dielectric barrier discharge (DBD) coupled with Fe-based zeolite catalyst was used to treat ammonia nitrogen and phenol wastewater. This experiment mainly investigated the effects of discharge voltage, discharge frequency, zeolite dosage, initial solution concentration and pH on ammonia nitrogen or phenol removal. Results showed that the removal rate of ammonia nitrogen increased with increased discharge voltage, discharge frequency, zeolite dosage, and initial pH and decreased with increased initial ammonia nitrogen concentration. The best removal rate of ammonia nitrogen reached 75.11%, which was higher than removal rates of the solutions treated with zeolite adsorption alone (10.93%) and DBD discharge alone (9.67%). However, the removal rate of phenol increased with discharge voltage, discharge frequency, and zeolite dosage and decreased with increased initial phenol concentration and initial solution pH. After 20 min of reaction, the removal rate of phenol reached 56.67%, which was higher than the removal rates of the solutions treated with zeolite adsorption alone (20.61%) and DBD discharge alone (3.54%).Therefore, a DBD-coupled metal zeolite catalyst system has a good treatment effect on inorganic and organic wastewater. In addition, DBD-coupled Fe-based zeolite catalyst was used to simultaneously treat mixed ammonia nitrogen and phenol wastewater. The degradation process and mechanism of mixed ammonia nitrogen and phenol wastewater in the system were studied to reflect the synergistic effect of the system.

High-performance electrospinning-phase inversion composite PDMS membrane for extractive membrane bioreactor: Fabrication, characterization, optimization and application

This study introduced a facile approach for high-performance electrospinning-phase inversion composite membrane, aiming at solving the low mechanical property, low mass transfer and salt leakage in extractive membrane bioreactor (EMBR) for phenol saline wastewater treatment. Composite membrane was fabricated through coating polydimethylsiloxane (PDMS) on electrospun PDMS membrane via dry phase inversion. Its surface was similar to that of phase inversion membrane while the cross section was uniformly distributed electrospun fibers in phase inversion layer, forming interconnected pore. The loose porous structure and high porosity were suitable for phenol permeation, and hydrophobic surface could reject the salt invasion. The tensile strength and elongation at break of composite membrane (56.5 μm thickness) were 1.7 MPa and 60.0%, making it stably operated in EMBR. Effects of different process variables were investigated, including membrane thickness, phenol concentration and wastewater flow rate. Remarkable performance of phenol biodegradation and salt rejection was achieved during EMBR operation, where the maximal phenol removal rate and conductivity variation in microorganism side were 508.9 mg L−1 d−1 and <0.1 ms cm−1, respectively. The highest phenol mass transfer coefficient of 8.8 × 10−7 m s−1 was achieved. It is reasonable to believe that this study fabricate a promising alternative membrane for EMBR application.

Application of vacuum-ultraviolet (VUV) for phenolic homologues removal in humic acid solution: Efficiency, pathway and DFT calculation

Vacuum-ultraviolet (VUV) photo-initiated oxidation of phenolic homologues in simulative natural water were investigated, including phenol, o-dihydroxybenzene (ODB), m-dihydroxybenzene (MDB), p-dihydroxybenzene (PDB), paranitrophenol (PNP) and o-chlorophenol (OCP). Results showed the phenolic homologues removal rate reached at least 90% in pure water, which was dependent on temperature, pH, concentration of HA, and functional group of HA. Experimental results indicated that 0.2 mg/L HA might be a critical point. Additionally, the rate constant of the six phenolic homologues reduced by 76.85%, 77.81%, 71.91%, 79.15%, and 55.69%, respectively in the MDB solution, and 79.73%, 82.80%, 95.36%, 80.38%, and 92.64%, respectively in the benzoic acid (BA) solution, compared to the rate constant in pure water. Moreover, quantum chemistry calculation indicated that the variances between phenolic compounds in removal rate were attributed to the substituent on the benzene ring. And, to some extent, the carboxy group of HA was supposed to arose the suppression for phenolic homologues removal rate. Mechanism involved phenolic homologues degradation using vacuum-ultraviolet (VUV) was summarized, where it underwent the formation of quinone structures, ring opening, short-chain organic acid, even eventually the transformation into NO3− and Cl− of PNP and OCP.

Removal of Phenol from Steel Plant Wastewater in Three Dimensional Electrochemical (TDE) Process using CoFe2O4@AC/H2O2

Abstract This study investigated the removal of phenol from steel industry wastewater by three dimensional electrochemical (TDE) process using CoFe2O4 nanobiocomposite based activated carbon in the presence of H2O2 (EC-CoFe2O4@AC-H2O2). In this study, CoFe2O4 nanobiocomposite-foundation activated carbon (CoFe2O4@AC) was used as microelectrode, adsorbent, and activator for peroxide hydrogen. The removal efficiency of phenol and COD was investigated through the parameters of pH, contact time, CoFe2O4@AC dosage, current density, and H2O2 concentration. The highest removal rates of phenol and COD were &gt;99% and 98%, respectively. Also, steel plant wastewater under the optimal conditions of pH = 6.5, current density = 15 mA cm−2, contact time = 25 min, H2O2 concentration of 1.0 mM, and CoFe2O4@AC dose = 0.3 g L−1. Kinetic analysis revealed that the adsorption experimental data was best fitted by the pseudo-first-order model.

3-D hierarchical Ag/ZnO@CF for synergistically removing phenol and Cr(VI): Heterogeneous vs. homogeneous photocatalysis

Synergistic photocatalysis offers great potential for simultaneously treating organic and heavy metal pollutants. Although considerable progress has been made, this technology is seriously restricted by the poor photoactivity of heterogeneous catalysts, and the contribution from homogeneous intermoleculars has been overlooked. In this paper, the Ag/ZnO@CF with 3-D hierarchical porous structure was fabricated and used to synergistically remove phenol and Cr(VI) from water. Due to the enhanced mass transfer and cocatalysts-facilitated charge separation, 3-D photocatalysts exhibited significantly improved activity for heterogeneous photocatalysis. Furthermore, both experimental characterizations and DFT calculations evidenced the formation of phenol-chromate(VI) esters with ligand-to-metal charge transfer from benzene ring to central chromium ion under photoexcitation. Thereafter, the effects of heterogeneous and homogeneous photocatalysis on the treatment efficiency of multiplex pollutants were investigated. In an ideal scenario, 2.4 and 2.3 times higher phenol and Cr(VI) removal rate were achieved compared to single catalytic reactions. This work not only offers new material strategy for photocatalyst exploration, but also provides new insights into the multiphase homogeneous catalysis contributed by intermolecular interactions.

Alcohol solvothermal reduction for commercial P25 to harvest weak visible light and fabrication of the resulting floating photocatalytic spheres

In this study, to fabricate stable floating photocatalytic spheres, facile alcohol solvothermal reduction was first employed to modify commercial TiO2 (P25) photocatalysts to harvest visible light and improve their performances for photodegrading phenol in seawater exciting by visible light. Floating photocatalytic spheres were then prepared by loading reduced P25 photocatalysts on inner and outer surfaces of acrylic hollow spheres. The structural characterizations showed that reduction of P25 introduced disorder–crystalline shell–core structures with present Ti3+ in reduced P25 photocatalysts. These features facilitated visible light response and phenol degradation in seawater under visible light irradiation. As reduction time or temperature of alcohol solvothermal process rose, more Ti3+ and shell–core structures were introduced into reduced P25, resulting in higher performances towards phenol degradation in seawater. However, extended periods of time and elevated temperatures decreased disordered layer of reduced P25, deteriorating the photocatalytic performances. Thanks to good light transmission of the hollow spheres and the high performance of the reduced P25, the photocatalytic performances of spheres loaded with reduced P25 could effectively degrade phenol in seawater even at low concentrations. The removal rate of phenol by floating spheres reached more than 95% after 8 h. In addition, the floating spheres displayed good stability and convenient reusability after six repeated photocatalytic degradation for phenol in seawater, promising features for future treatment of organic pollutants in oceans.

Modelling and optimization of photocatalytic degradation of phenol via TiO2 nanoparticles: An insight into response surface methodology and artificial neural network

The epidemic growth of the pharmaceuticals industries over the years in order to meet the human demands had exerted substantial pressure on the global environment, particularly water pollutions crisis. Herein, the photocatalytic degradation of phenol was investigated via commercial TiO2 nanoparticles. The Artificial Neural Network (ANN) and Response Surface Methodology (RSM) was employed for scrutinizing the suitable modelling and optimized condition of the TiO2 nanoparticles in yielding a profound rate of phenol removal. The parameters of investigation involved pH, phenol concentration, catalyst doses and degradation time. The RSM data shows the profound rate of phenol removal ˜ 99.48% was achieved by TiO2 NPs in a designed photocatalytic system that set at 5.42 pH, 15.21 mg/L phenol concentration, 1.75 g/L TiO2 dosage and 540 min irradiation time. The designed system fits well with the Pseudo-First-Order and the Langmuir isotherm model with R2 > 0.999. On the other hand, the ANN study revealed that the predicated model was perfectly fitted with the experimental data giving the highest value of R2. This work provides an insight into two different statistical modelling and optimization which could provide exposure for developing an optimized nanomaterial towards the removal of hazardous pollutant.

Enhancing electrochemical degradation of phenol at optimum pH condition with a Pt/Ti anode electrode

ABSTRACT Electrochemical phenol degradation using a platinum-coated Ti electrode was comparatively investigated at different pH levels, which were maintained over the entire operation period. Various analyses such as phenol concentration, TOC, COD, cyclic voltammetry, and total current efficiency were conducted to determine the performance of phenol degradation in the presence of Na2SO4 as the electrolyte. The phenol and COD removal rate were relatively higher at lower pH conditions (pH 3 and 5) due to high oxidant generation of OH radical and H2O2. At pH 5 condition, phenol (90 mg L−1) was completely removed after a 24-h operation. However, complete COD removal was obtained after about 250-h operation, due to byproduct formations (hydroquinone and polymers) during the phenol degradation. Cyclic voltammetry analysis indicated that acidic conditions could inhibit the oxygen-evolution reaction, causing an increase in current efficiency and a decrease in energy consumption. This study suggests that phenol-contaminated wastewater can be efficiently treated by an electrochemical process using a Pt/Ti electrode with continuously controlled lower pH conditions.Phenol oxidation by electrochemical treatment system at different pH conditions Electrochemical reactor (inside) R: reference electrode, A: Pt/Ti anode, C: Ti cathode, G: pipe to the gas bag, S: sample holder, M: magnetic stirrer

Enhanced performance of TiO2/reduced graphene oxide doped by rare-earth ions for degrading phenol in seawater excited by weak visible light

La3+- or Yb3+-doped TiO2 supported on the surface of reduced graphene oxide were fabricated by adsorbed-layer nanoreactor synthesis (ANS) coupling with a solvothermal treatment to extend photocatalysis application in the advanced treatment of simulated wastewater with high salt concentration. Results showed that La3+ or Yb3+ could distribute in the TiO2 lattice, only in ANS preparation with graphene oxide as the carrier, to replace Ti4+ during the solvothermal treatment, thus introducing TiO2 mixed-crystal and heterojunction structures in the catalysts. La3+ or Yb3+ caused lattice distortion structures and anionic vacancies in the TiO2 lattice. The anionic vacancies (oxygen vacancies) might generate Ti3+ in catalysts, thus enhancing visible-light response, due to impurity levels introduced by La3+ or Yb3+. As the strong adsorption capability of the catalyst for phenol was not interfered by salt ions in the simulated wastewater, the catalysts could efficiently degrade phenol. The highest removal rate of phenol was approximately 90%.

Rapid one-pot microwave-hydrothermal synthesis of OMS-2 and full-solar-spectrum photocatalytic performance for high phenol concentration

A new rapid and simple synthesis method of cryptomelane-type octahedral molecular sieve (OMS-2) was proposed, which only required KMnO4 and H2SO4 as reactants and a controlled microwave hydrothermal process. The crystallinity and particle size of OMS-2 were found to gradually increase with the synthesis temperature and time, while the specific surface area decreased. Moreover, the synthesis of pure OMS-2 only required about 5 min at 180 °C, which is a lower synthesis time than those of previously reported methods. For the high concentration (100 mg/L) of phenol degradation under full-solar-spectrum irradiation, the removal rates of phenol were all in the range of 67%−73%, but the removal rates of total organic carbon were between ∼40% and ∼60%. This indicates that the synthesized OMS-2 had a similar high photocatalytic performance for phenol in a wide temperature and time range. And it can be suitable for industrial application.

Enhanced treatment of coal gasification wastewater in a membraneless sleeve-type bioelectrochemical system

A bioelectrochemical system (BES) is a technology with potential for accelerating the degradation of recalcitrant compounds, the components and configurations of which are important for treatment performance. In the present work, a membraneless sleeve-type BES (termed BioE) was designed for the treatment of synthetic coal gasification wastewater (CGW, phenol as a model pollutant) and real CGW. Compared with the biological control (termed Bio), the phenol removal rate and COD removal efficiency increased by 2.6 and 2.1 fold in the BioE, respectively. However, the coulombic efficiency of this system was relatively low, ranging from 0.42% to 2.6%. This combination of results indicated that anode respiration was not the main process in the BioE. The increased CH4 production and higher levels of methanogens obtained from the BioE confirmed that the methanogenic process proceeded, possibly facilitated by the diffusion of H2 from the cathode to the anode. This study provides new insight into biocathode function for COD oxidation removal in BESs. Moreover, this study indicates that pursuing a high coulombic efficiency may not be necessary for wastewater treatment, as it consumes less energy at the lower value.

Enhancing effects of activated carbon supported nano zero-valent iron on anaerobic digestion of phenol-containing organic wastewater

Activated carbon supported nano zero-valent iron material (NZVI/AC) was prepared and added to an anaerobic digestion tank to reduce the toxicity inhibition of phenols and increase the methane yield of phenol-containing organic wastewater (POW). The anaerobic digestion (AD) characteristics, including conversion rate of organic substances, removal rate of phenol, and methane yield of POW with different concentrations of phenol were studied, and moreover, the enhancing effects of NZVI/AC on the AD of POW were focused. When the concentration of phenol was below 500 mg/L, the methane yield from AD of POW was 387.5 mL, which was 10.71% higher than that from control organic water without phenol, however, phenol concentrations greater than 1000 mg/L severely inhibited AD, and methane yield was only 50% of the control sample. Indicating that anaerobic microorganisms had a certain degree of tolerance to phenol, and low concentration of phenol could promote AD of organic water although the phenol with high concentration showed severe inhibition. The methane yield increased due to the probable conversion of phenol to methane by microbial actions. In the AD of POW with 500 mg/L phenol, the conversion rate of organic substances increased from 37.49% (control group without any accelerant) to 66.56% after adding NZVI/AC. The removal rate of phenol also increased from 39.03% to 81.32%. Cumulative methane yield increased by 145.5%–810 mL compared with the control group. The AC carrier in NZVI/AC exerted a good adsorption effect on phenols, reducing the concentration of phenols in the solution and thus minimizing their toxic effects on microbial activity. The NZVI loaded on AC particles strengthened the electron transfer between methanogens by its good electrical conductivity, and then promoted the AD performance of organic matter. Furthermore, NZVI exerted a micro-electrolytic effect on phenolic substances, which could increase the removal rate of phenol. Therefore, NZVI/AC could be used as an efficient accelerant for the AD of POW to enhance the AD process.

Comparison on efficiency of electrochemical phenol oxidation in two different supporting electrolytes (NaCl and Na2SO4) using Pt/Ti electrode

Abstract The electrochemical oxidation of phenol was evaluated with two different electrolytes using a Pt/Ti anode electrode in a single-chambered reactor. The bulk electrolysis was conducted at a fixed current density of 9.6 mA cm−2, and the average applied potential difference was 6 V (anode potential 4 V; cathode potential -2 V). The feasibility of electrochemical treatment of phenol contaminated water was determined in terms of phenol degradation rate, byproduct formation, pH stability, and current efficiency. Galvanostatic electrolysis with NaCl electrolyte removed phenol and chemical oxygen demand (COD) faster than with Na2SO4 electrolyte, possibly due to the formation of chloride–oxychloride radicals, which are strong oxidation agents. The phenol and COD removal rates with NaCl were 2.26 × 10 − 2 and 3.00 × 10 − 4 min−1, which was 9.5 and 1.5 times higher respectively than with Na2SO4. Energy consumption and current efficiency during the electrolysis suggested that chloride ions hinder the oxygen-evolution reaction, causing a growth in current efficiency and a decrease in energy consumption. This result clearly indicated that the presence of chloride in the solution was an important parameter for the efficient electrochemical oxidation of phenol-contaminated water.

Study of the mechanisms underlying the effects of composite intermediate layers on the performance of Ti/SnO2-Sb-La electrodes

To mitigate the drawback of the short service life of titanium-based SnO2 electrodes, we prepared Ti/SnO2SbLa electrodes by the sol-gel method with two kinds of CeMn and FeMn composite intermediate layers, a Mn intermediate layer, or no intermediate layer. The surface structure and morphology of the prepared electrode coating were characterized by scanning electron microscopy (SEM), X-ray diffraction (XRD), and X-ray photoelectron spectroscopy (XPS), and the influence of the composite intermediate layer on the electrochemical performance of the electrode and the electrocatalytic oxidation of phenol were analysed by cyclic voltammetry, anodic linear voltammetry, AC impedance spectroscopy and Mott-Schottky curve tests; additionally, accelerated lifetime tests were performed for electrodes with different intermediate layers. The experimental results show that, compared to electrodes with the Mn interlayer or no intermediate layer, the electrode with the CeMn composite intermediate layer had markedly improved electrochemical performance and oxygen evolution potential, and the highest oxygen evolution potential could reach 1.84 V. Moreover, the capacity for electrocatalytic oxidation degradation of phenol was enhanced to some degree, with the highest removal rate of phenol reaching 93.6% after treatment for 180 min, and the maximum removal rate of COD can reach 77.92%. In the process of degrading phenol, the cell voltage of the electrode is kept to a minimum, and the stability is maximized. Accelerated lifetime testing showed that, compared with that of the no-intermediate-layer electrode, the lifetime of the electrode with the CeMn composite intermediate layer was increased 5-fold, with the longest lifetime reaching 85 min. Therefore, the CeMn composite intermediate layer can effectively improve the service life of electrodes based on titanium and tin.

Hydrothermal reduction of commercial P25 photocatalysts to expand their visible-light response and enhance their performance for photodegrading phenol in high-salinity wastewater

This study aimed to expand the visible-light response of commercial titanium dioxide (TiO2, P25) photocatalysts using surface modification by hydrothermal reduction with various reductants to improve their photocatalytic performance for phenol degradation in high-salinity wastewater under room visible-light irradiation. Structure characterization results for different reduced P25 photocatalysts show that hydrothermal reduction cannot only generate disordered crystalline shell–core structures on the catalyst surface but also introduce several Ti3+ into the photocatalysts, facilitating the visible-light response of reduced P25. The moderate conditions of hydrothermal reduction not necessarily destroyed the inner crystalline structure of P25 to form amorphous TiO2 as deep trapping sites for photogenerated charges, different from the results for the reduced P25 obtained by hydrogeneration reduction (P25–H2). Therefore, the reduced P25 obtained by hydrothermal reduction with Zn as reductant featured a slightly higher photocatalytic activity for phenol than P25–H2 under visible-light irradiation, although P25–H2 exhibited a smaller Eg and stronger visible-light absorbance. The highest removal rate for phenol of reduced P25 within 5 h reached up to 87.5% and considerably exceeded that of P25–H2 (60.0% removal rate of phenol). Apart from the reduction capability of metals, the solubility of the corresponding metal hydroxide plays a major role in P25 reduction in the hydrothermal process. The water-insoluble metal hydroxide precipitates on the metal surface and inhibits the reduction between metal and P25, thereby decreasing the photocatalytic performance of reduced P25 for phenol excited by room visible-light.