Mineralization Of Phenol Research Articles

Revealing the Role of Elementary Doping in Photocatalytic Phenol Mineralization

Photocatalytic mineralization of recalcitrant contaminants like phenol in wastewater requires abundant hydroxyl radicals (•OH) to initiate the reaction prior to the ring-opening. We here increase the free energy for adsorption of O* species on TiO2 surface and slightly downshift the band position by tin doping. This can simultaneously promote the generation and suppress the annihilation of •OH. Besides, tin doping can also facilitate semiconductor-cocatalyst-solution (SCS) interfacial electron transfer by lowering the potential barrier and synergistically enhance the photon utilization. By filming the photocatalyst onto our developed fixed bed reactors, the loss of photons resulting from undesirable absorption by contaminants can be alleviated. By these virtues, trace amount of phenol in wastewater can be efficiently mineralized.

Electron self-sufficient core-shell BiOCl@Fe-BiOCl nanosheets boosting Fe(III)/Fe(II) recycling and synergetic photocatalysis-Fenton for enhanced degradation of phenol

Core-shell BiOCl@Fe-BiOCl nanosheets with electron self-sufficient structure were prepared as catalysts to promote degradation and mineralization of phenol through synergetic photocatalysis-Fenton. This electron self-sufficient structure was established by engaging a strong internal electric field of BiOCl core and electron-capture centers of doped Fe(III) in Fe-BiOCl shell for electrons supplying and consuming, respectively, separating charges spatially and enriching holes on the surface of catalysts. Meanwhile, the Fe(III) transited to Fe(II), which acted as reactive sites for H2O2 activation and was further reversed to Fe(III) and hydroxyl radical (•OH) through Fenton reaction, achieving Fe(III)/Fe(II) recycling. The •OH and surface holes could synergistically boost the degradation and mineralization (∼64 %) of phenol. The reaction rate constant of BiOCl@Fe-BiOCl nanosheets was ∼41.32 and ∼95 times higher than that of BiOCl under full spectra and visible light irradiation, respectively. This work provides sophisticated structure design of catalysts, boosting Fe(III)/Fe(II) recycling, catalytic activity, and mineralization.

Heterogeneous catalytic ozonation for highly efficient mineralization of phenol with La-modified Ce/γ-Al<sub>2</sub>O<sub>3</sub>

In this study, La-Ce/γ-Al<sub>2</sub>O<sub>3</sub> materials for the catalytic ozonation of phenol were prepared by impregnation. In order to analyze the physicochemical properties, BET, SEM, XRD, XPS, and FTIR were used to characterize the catalysts. The removal performance of phenol under different reactive conditions (catalyst dosage, initial pH value, initial phenol concentration, and ozone concentration) was investigated, and the possible catalytic oxidation mechanism and conversion pathway of phenol were proposed through the analysis of ROS and intermediates in solution. The results indicated that the conversion rate of 2.5% La-Ce/γ-Al<sub>2</sub>O<sub>3</sub> increased by 20.53% within 20 min compared with ozonation alone. Moreover, the CO<sub>2</sub> mineralization rate was more than twice that of ozonation alone within 250 min, reaching 92.53%, and superior CO<sub>2</sub> mineralization was maintained after repeated use. The CO<sub>2</sub> mineralization rate of phenol after adding 3 g/L 2.5% La-Ce/γ-Al<sub>2</sub>O<sub>3</sub> catalyst reached almost 100%, and could be maintained in a solution with a wide pH range of 3~9.5. From the characterization results, it could be seen that the 2.5% La-Ce/γ-Al<sub>2</sub>O<sub>3</sub> catalyst obtained higher adsorbed oxygen and hydroxyl species content than γ-Al<sub>2</sub>O<sub>3</sub> and Ce/γ-Al<sub>2</sub>O<sub>3</sub>. In the process of phenol catalyzed ozonation, the •O<sub>2</sub>ˉ species in the solution were deduced to be the key ROS.

Hybrid peroxi-coagulation/ozonation process for highly efficient removal of organic contaminants

Aromatic compounds such as phenols presented widely in coal chemical industry wastewater (CCW) render the treatment facing great challenge due to their biorefractory characteristics and potential risks to the environment and human health. Ozone-based advanced oxidation processes show promising for these pollutants removal, but the mineralization via ozonation alone is unsatisfactory and not cost-effective. Herein, a hybrid peroxi-coagulation/ozonation process (denoted as PCO) was developed using sacrificial iron plate as an anode and carbon black modified carbon felt as cathode in the presence of ozonation. An enhanced phenol removal of ∼100% within 20 min and phenol mineralization of ∼80% within 60 min were achieved with a low energy consumption of 0.35 kWh/g TOC. In this novel process, synergistic effect between ozonation and peroxi-coagulation was observed, and beside O3 direct oxidation, peroxone played a dominant role for phenol removal. In the PCO process, the hydrolyzed Fe species enhanced the generation of reactive oxygen species (ROS), while •OH was dominantly responsible for pollutant degradation. This process also illustrated high resistance to high ionic strength and better performance for TOC removal in real wastewater when compared with ozonation and peroxi-coagulation process. Therefore, this process is more cost-effective, being very promising for CCW treatment.

Mathematical analysis of a two-tiered microbial food-web model for the anaerobic digestion process.

In this research paper, we presented a four-dimensional mathematical system modeling the anaerobic mineralization of phenol in a two-step microbial food-web. The inflowing concentrations of the hydrogen and the phenol are considered in our model. We considered the case of general class of nonlinear growth kinetics, instead of Monod kinetics. Due to some conservative relations, the proposed model was reduced to a two-dimensional system. The stability of the steady states was carried out. Based on the species growth rates and the three main operating parameters of the model, represented by the dilution rate and input concentrations of the phenol and the hydrogen, we showed that the system can have up to four steady states. We gave the necessary and sufficient conditions ensuring the existence and the stability for each feasible equilibrium state. We showed that in specific cases, the positive steady state exists and is stable. We gave numerical simulations validating the obtained results.

Homogeneous interfacial electron transfer promotes photoinduced hole extraction for phenol mineralization

We here developed a fixed-bed photocatalyst based on homogeneous contact that can synergistically promote the generation of hydroxyl radicals by facilitating semiconductor–cocatalyst-solution interfacial electron transfer.

Catalytic ozonation of phenol by magnetic Mn0.7Ce0.3Ox/CNT@Fe3C

A high-efficient and stable catalyst is highly desired to catalyze ozone for refractory organic pollutants removal. In this work, Mn-Ce bimetallic oxide loaded CNT@Fe3C (Mn0.7Ce0.3Ox/CNT@Fe3C) was synthesized with Mn0.7Ce0.3Ox as the active component and magnetic CNT@Fe3C as the support. The catalytic performance of Mn0.7Ce0.3Ox/CNT@Fe3C towards catalytic ozonation was evaluated. The TOC removal efficiency of phenol degradation after 45 min of reaction was 98%, which was 1.5 times and 1.8 times that of monometallic CeO2/CNT@Fe3C (65%) and MnxOy/CNT@Fe3C (54%), respectively. The synthesized-Mn0.7Ce0.3Ox/CNT@Fe3C possessed good reusability during five successive cycles and remained efficient over a wide range of pH 4.2–8.3. The results of EPR measurements and quenching experiments demonstrated that hydroxyl radicals (·OH) were the dominant reactive oxidation species (ROS) for phenol mineralization in the Mn0.7Ce0.3Ox/CNT@Fe3C/O3 system. Moreover, the magnetic Mn0.7Ce0.3Ox/CNT@Fe3C is easily recovered and reused.

Resource utilization of bovine bone to prepare biochar as persulfate activator for phenol degradation

Designing non-metallic catalyst as persulfate (PS) activator for effective organic pollutants degradation in water is challenging. Herein, bovine-derived bone chars (BBCs) were prepared with different temperatures (300, 500 and 700 °C), which contained ordered mesoporous structures, thus realizing great phenol uptake (149.84 mg/g) with 100% degradation in combination with PS within 180 min. Furthermore, both reactive species (SO4•−; ·OH, O2•− and 1O2) and electron transfer process contributed to phenol removal due to the abundant defects and functional groups on BBC700. Owing to the multiples mechanisms, the BBC700/PS system exhibited an excellent phenol mineralization rate of 89.6 ± 1.85%, accompanied by strong anti-jamming capacity to relatively extensive pH range (3.0–7.0), various co-existing constituents and water bodies. Additionally, DFT calculations and GC-MS were used to illustrate the 7 kinds of degradation intermediates and the overall toxicity was efficiently alleviated, thus proposing a tailored non-metallic catalyst with great potential in water purification.

Degradation of phenolic pollutants by persulfate-based advanced oxidation processes: metal and carbon-based catalysis

Abstract Wastewater recycling is a solution to address the global water shortage. Phenols are major pollutants in wastewater, and they are toxic even at very low concentrations. Advanced oxidation process (AOP) is an emerging technique for the effective degradation and mineralization of phenols into water. Herein, we aim at giving an insight into the current state of the art in persulfate-based AOP for the oxidation of phenols using metal/metal-oxide and carbon-based materials. Special attention has been paid to the design strategies of high-performance catalysts, and their advantages and drawbacks are discussed. Finally, the key challenges that govern the implementation of persulfate-based AOP catalysts in water purification, in terms of cost and environmental friendliness, are summarized and possible solutions are proposed. This work is expected to help the selection of the optimal strategy for treating phenol emissions in real scenarios.

Continuous Fe(II)-dosing scheme for persulfate activation: Performance enhancement mechanisms in a slurry phase reactor

Mechanisms involved in the superior performance of the continuous Fe2+ dosing scheme over the single Fe2+ dosing scheme was thoroughly investigated. The kinetics and stoichiometry of the phenol removal/persulfate consumption strongly depended on the volumetric or molar Fe2+ feeding rate, Fe2+ concentration in the feed solution, and Fe2+ feeding mode (continuous or single dose). The process performance was determined by the molar Fe2+ feeding rate rather than the volumetric Fe2+ feeding rate or the Fe2+ concentration in the feed solution. The phenol degradation rate increased as the molar Fe2+ feeding rate increased to 2.77 mmol/min but decreased as the Fe2+ feeding rate increased further. The sulfate radical was predominant radical species formed in continuous Fe2+ dosing mode. The hydroxyl and sulfate radicals were both important in single Fe2+ dose mode. The presence of hydroxyl radicals in single Fe2+ dosing mode decreased the amount of phenol oxidation that occurred, probably because the hydroxyl radicals were readily scavenged by soil organic matter. Continuous Fe2+ dosing facilitated phenol mineralization, which was indicated by total organic carbon measurements and toxicity tests performed using Hyalella azteca.

Photodegradation and Mineralization of Phenol Using TiO2Coated γ-Al2O3: Effect of Thermic Treatment

It is well-known that γ-Al2O3 possesses large, specific areas and high thermal, chemical, and mechanical resistance. Due to this, it is the most-used support for catalysts, in this case TiO2, as it enables it to achieve better dispersion and improves the activity in catalytic photodegradation reactions. In a previous work, it was observed that the optimal content of TiO2 in γ-Al2O3 was around 15% since the degradation of phenol results were maximized and a synergistic effect was generated by the interaction of both oxides. In addition, an increase in acidity crystal size and the generation of localized, oxygen-vacant, electronic states in the forbidden band of γ-Al2O3, were observed. This study focuses on the effect of the calcination temperature on a γ-Al2O3-TiO2 catalyst (15% w/w of TiO2) and its impact on photocatalytic activity. The catalysts prepared here were characterized by X-ray diffraction, N2 adsorption–desorption, FTIR-pyridine adsorption, MAS-NMR, HRTEM-FFT, UV-vis, and fluorescence spectroscopy.

Plasmonic effect and bandgap tailoring of Ag/Ag2S doped on ZnO nanocomposites for enhanced visible-light photocatalysis

Ag/Ag2S-ZnO nanocomposites were prepared via a simple hydrothermal process followed by a plasmonic Ag+ reduction through a photo-deposition method. Ag2S was introduced to narrow the overall composite bandgap and activate the surface plasmon resonance (SPR) effect of the Ag+ cation present. The physicochemical properties of the as-synthesised catalysts were characterised by X-ray diffraction (XRD), scanning and transmission electron microscopies (SEM and TEM), Brunauer-Emmett-Teller (BET) analysis. Fourier-transform infrared spectroscopy (FTIR), Ultraviolet diffuse reflectance spectroscopy (UV–vis DRS), photoluminescence emission spectra (PL) and X-ray photoelectron spectroscopy (XPS) was conducted to investigate the photo-absorption and emission spectra of the nanocomposites. The degradation efficiency of all the synthesised catalysts (ZnO, Ag2S, Ag/ZnO and Ag2S/ZnO) prior to the final product, Ag/Ag2S/ZnO was tested and compared. Results showed that the ternary Ag/Ag2S/ZnO achieved a 98 % phenol removal compared to 50 %, 11 %, 64 % and 93 % for ZnO, Ag2S, Ag/ZnO and binary Ag2S/ZnO, respectively. The degradation kinetics followed the Langmuir-Hinshelwood model, which typically describes heterogeneous photocatalytic surface reactions. The linear fits had R2 values higher than 0.97, which confirms the degree of accuracy or statistical fitness to the kinetic model. Degradation scavenger test confirmed the holes (h+) as the main inhibitor and identified the superoxide O2•¯ radical as the main active specie responsible for the degradation. Total organic carbon analysis using the ternary Ag/Ag2S-ZnO catalyst only achieved a 74% phenol mineralization after 24 h of photocatalysis. Recyclability tests showed good phenol removal stability of Ag/Ag2S-ZnO at 41 % after five recycle runs. Hence, a synergistic degradation mechanism responsible for the efficient photo-degradation performance was proposed.

One-step preparation of RGO/Fe3O4\u2013FeVO4 nanocomposites as highly effective photocatalysts under natural sunlight illumination

The study used a one-step hydrothermal method to prepare Fe3O4–FeVO4 and xRGO/Fe3O4–FeVO4 nanocomposites. XRD, TEM, EDS, XPS, DRS, and PL techniques were used to examine the structurally and morphologically properties of the prepared samples. The XRD results appeared that the Fe3O4–FeVO4 has a triclinic crystal structure. Under hydrothermal treatment, (GO) was effectively reduced to (RGO) as illustrated by XRD and XPS results. UV–Vis analysis revealed that the addition of RGO enhanced the absorption in the visible region and narrowed the band gap energy. The photoactivities of the prepared samples were evaluated by degrading methylene blue (MB), phenol and brilliant green under sunlight illumination. As indicated by all the nanocomposites, photocatalytic activity was higher than the pure Fe3O4–FeVO4 photocatalyst, and the highest photodegradation efficiency of MB and phenol was shown by the 10%RGO/Fe3O4–FeVO4. In addition, the study examined the mineralization (TOC), photodegradation process, and photocatalytic reaction kinetics of MB and phenol.

Complete mineralization of phenolic compounds in visible-light-driven photocatalytic ozonation with single-crystal WO3 nanosheets: Performance and mechanism investigation

Complete mineralization of phenolic compounds into CO2 and H2O is desirable for removing them in wastewater, but it is challenging due to the generated recalcitrant intermediates, which requires highly effective advanced oxidation process with proper catalysts. Herein, we found that single-crystal WO3 nanosheets (NSs)-based photocatalytic ozonation (PCO) can realize complete mineralization of phenols (phenol and 2-chlorophenol) under visible light irradiation. Almost 100% mineralization ratio of phenols was achieved through WO3 NSs-based PCO system within short time. By comparing their performances with those of polycrystalline WO3 nanoparticles, detecting and analyzing the intermediates, identifying the dominant radicals and conducting some electrochemical characterizations, the origin of superior catalytic activity of WO3 NSs was uncovered, the mineralization pathways and the overall mechanism were proposed. The excellent PCO performance of WO3 NSs was contributed to their nanosheet morphology with single-crystal microstructure and good dispersion, which can provide continuous interior channels for the photogenerated charge transport from the bulk to surface of WO3 NSs and enough active sites for the surface reactions triggered by these charges. This work puts forwards new ideas to design highly active photocatalysts for PCO and helps deepen understanding of the catalytic mechanism of PCO.

Environment-Friendly Catalytic Mineralization of Phenol and Chlorophenols with Cu- and Fe- Tetrakis(4-aminophenyl)-porphyrin—Silica Hybrid Aerogels

Fenton reactions with metal complexes of substituted porphyrins and hydrogen peroxide are useful tools for the mineralization of environmentally dangerous substances. In the homogeneous phase, autooxidation of the prophyrin ring may also occur. Covalent binding of porphyrins to a solid support may increase the lifetime of the catalysts and might change its activity. In this study, highly water-insoluble copper and iron complexes of 5,10,15,20-tetrakis(4-aminophenyl)porphyrin were synthesized and bonded covalently to a very hydrophilic silica aerogel matrix prepared by co-gelation of the propyl triethoxysilyl-functionalized porphyrin complex precursors with tetramethoxysilane, followed by a supercritical carbon dioxide drying. In contrast to the insoluble nature of the porphyrin complexes, the as-prepared aerogel catalysts were highly compatible with the aqueous phase. Their catalytic activities were tested in the mineralization reaction of phenol, 3-chlorophenol, and 2,4-dichlorophenol with hydrogen peroxide. The results show that both aerogels catalyzed the oxidation of phenol and chlorophenols to harmless short-chained carboxylic acids under neutral conditions. In batch experiments, and also in a miniature continuous-flow tubular reactor, the aerogel catalysts gradually reduced their activity, due to the slow oxidation of the porphyrin ring. However, the rate and extent of the degradation was moderate and did not exclude the possibility that the as-prepared catalysts, as well as their more stable derivatives, might find practical applications in environment protection.

Photocatalytic mineralization of phenol by Sn-modified calcites

Calcium-based photocatalysts represent an economic and available alternative for the photodegradation of distinct pollutants such as pesticides, pigments, colorants, and drugs, among others. In the following paper, the morphological, structural, optical, and textural properties of a series of materials based on calcium carbonate (calcite) modified with Tin and their evaluation in phenol photodegradation were studied. The synthesized materials were characterized by several techniques, including X-Ray Diffraction (XRD), Fourier Transform Infrared Spectroscopy (FTIR), N2 adsorption–desorption at 196 °C, Diffuse Reflectance Spectroscopy (DRS), Scanning Electron Microscopy (SEM), and X-ray Photoelectron Spectroscopy (XPS). The characterization information indicated that a portion of Sn4+ was incorporated into calcite structure and the rest crystallized as SnO2. The effect of tin incorporation was also evidenced by the calculated bandgap values whereas the tin amount increased the values got close to SnO2 value. Neither the bare sample SnO2 nor CaCO3 presented photoactivity for phenol mineralization. Nevertheless, it was demonstrated that the modified calcites presented a photocatalytic activity comparable to P25-TiO2, carrying out phenol mineralization in 3 h. Tin-modified calcite compounds were obtained by a controlled coprecipitation method. The photocatalytic evaluations presented a photocatalytic activity comparable to P25-TiO2, which was assigned to tin presence in a low-value material such as calcite.

Deep degradation of pollutants by perylene diimide supramolecular photocatalyst with unique Bi-planar π-π conjugation

Perylene diimide (PDI) was subjected to terminal substitution with nicotinic acid (NA) to prepare a unique, bi-planar, π-π conjugated, ultrathin, porous supramolecular photocatalyst (hp-PDi-NA). The photocatalytic activity of hp-PDI-NA for phenol degradation under visible light was approximately 3.5 times that of nano-PDI. hp-PDI-NA exhibited prominent mineralization ability, inducing almost complete mineralization of phenol. The hp-PDI-NA supramolecular photocatalyst was highly stable and maintained 98% of its initial activity after five experimental cycles (35 h). hp-PDI-NA also showed strong degradation and mineralization ability for model antibiotics (oxytetracycline (OTC)), and hormones (ethinylestradiol (EE)). The small steric hindrance, double π-π conjugation effect, and existence of layered pores with a thickness of less than 1 nm shortened the distance between the supramolecular layers and effectively improved the transmission and separation of photogenerated carriers. Combined with theoretical calculations, a mechanism explaining the possible influence of the bi-planar structure on the photocatalytic activity was proposed. The results demonstrate that terminal substitution with aromatic compounds, instead of aliphatic compounds, is an important strategy for improving the performance of PDI supramolecular photocatalysts.

A Kinetic Study of Photocatalytic Degradation of Phenol over Titania–Silica Mixed Oxide Materials under UV Illumination

A set of titania–silica mixed oxide materials were prepared by a cosolvent-induced gelation method using ethanol and toluene as solvent and cosolvent, respectively. These materials were extensively characterized by utilizing several characterization techniques and assessed for phenol degradation under UV illumination. The degradation of phenol follows first-order kinetics, and fragmented products formed during the phenol degradation were qualitatively identified by using high performance liquid Chromatographic (HPLC) and atomic pressure chemical ionization mass spectroscopic (APCI-MS) techniques. The complete mineralization of phenol was further evidenced by the measurement of the total organic contents that remained in the solution after irradiation. The pore diameter of the materials was found to be the key factor for phenol degradation, whereas surface area and pore volume play a role among the mixed oxide materials. In addition, in the mixed oxide system there was an inverse correlation obtained with the particle size of the materials and the degradation efficiency. The smaller particle size of titania in the mixed oxide material was found to be a requirement for an effective degradation of phenol.

Efficient mineralization of phenol in high chloride solutions via Fenton reactions using γ-Cu2(OH)3Cl as a catalyst

γ-Cu2(OH)3Cl is used as a Fenton catalyst to mineralize phenol in high chloride solutions. The mineralization of phenol can be enhanced even at 15000 mg∙L–1 NaCl under ambient pH. In addition, other aromatic contaminants including bisphenol A, benzoic acid, 2-chlorophenol, salicylic acid and aniline can also be effectively mineralized under the high chloride concentration. However, reference catalysts including CuSO4, CuO and Cu2O are significantly depressed by chloride. The chloride resistance ability of γ-Cu2(OH)3Cl is proposed. First, σ-Cu-ligand complexes formed between Cu2+ and phenolic hydroxyl can react with H2O2 to promote the rapid reduction of Cu2+ to Cu+, which are not hindered by chloride. Second, the self-redox property of γ-Cu2(OH)3Cl which initiates the electron transfer from H2O2 to Cu2+ to generate Cu+ is improved by chloride. Third, the circumneutral pH could suppress HO• scavenging by chloride. The activation energies of phenol mineralization over γ-Cu2(OH)3Cl in chloride-free and high chloride solutions are 42.9 and 32.3 kJ∙mol–1, respectively. Chloride does not change the phenol mineralization pathway but accelerates its degradation into small carboxylic acids.

Epitaxial BiP5O14 layer on BiOI nanosheets enhancing the photocatalytic degradation of phenol via interfacial internal-electric-field

BiOI/BiP5O14 heterostructure with enhanced interfacial internal electric field for directional charge transfer and separation effectively were constructed successfully through epitaxial BiP5O14 layer on the surface of BiOI nanosheets. Dramatical enhanced internal electric field of BiOI/BiP5O14 heterostructure was established when BiP5O14 monolayer epitaxial grow on the surface of BiOI nanosheets by adding 2% of NaH2PO4. As a result, this heterostructure could boost the photodegradation and mineralization of phenol. Compared to pristine BiOI nanosheets, the photocatalytic reaction constant rates of phenol over the BiOI/BiP5O14 heterostructure were elevated over 8.5 times, and the corresponding mineralization ability was also enhanced 8.9 times due to the effective and directional charges transfer and separation. This work provides an evidential proof of rational designing heterostructure via epitaxial growth, and confirms the internal electric field drive charge transfer and separation directionally for promoted photocatalytic performances.