Selective Production of CO from Organic Pollutants by Coupling Piezocatalysis and Advanced Oxidation Processes

To date, the chemical conversion of organic pollutants into value-added chemical feedstocks rather than CO₂ remains a major challenge. Herein, we successfully developed a coupled piezocatalytic and advanced oxidation processes (AOPs) system for achieving the conversion of various organic pollutants to CO. The CO product stems from the specific process in which organics are first oxidized to carbonate through peroxymonosulfate (PMS)-based AOPs, and then the as-obtained carbonate is converted into CO by piezoelectric reduction under ultrasonic (US) vibration by using a Co₃S₄/MoS₂ catalyst. Experiments and DFT calculations show that the introduction of Co₃S₄ not only effectively promotes the transfer and utilization of piezoelectric electrons but also realizes highly selective conversion from carbonate to CO. The Co₃S₄/MoS₂/PMS system has achieved selective generation of CO in actual complex wastewater treatment for the first time, indicating its potential practical applicability.     

Fe-Mn-Cu-Ce/Al2O3 as an efficient catalyst for catalytic ozonation of bio-treated coking wastewater: Characteristics,efficiency, and mechanism

It is important to develop a catalyst that has high catalytic activity and can improve the degradation efficiency of refractory organic pollutants in the catalytic ozonation process. In this study, Fe-Mn-Cu-Ce/Al₂O₃ was synthesised via impregnation calcination for catalytic ozonation of bio-treated coking wastewater. The physical and chemical characteristics of the catalysts were analysed using X-ray diffraction (XRD), X-ray fluorescence spectrometry (XRF), X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM), and Brunauer–Emmett–Teller nitrogen adsorption–desorption methods. The effects of catalyst dosage, pH, and reflux ratio on the degradation efficiency of wastewater were examined in laboratory-scale experiments. The chemical oxygen demand (COD) removal rate of bio-treated coking wastewater was estimated to be 52.76 % under optimal conditions. The experiments on the catalytic mechanism demonstrated that the surface hydroxyl formed by the Lewis acid sites on the surface of the catalyst can react with ozone as the active site forming the active oxygen (·OH, ·O₂^–, and ¹O₂), thereby efficiently degrading the organic pollutants in coking wastewater. Furthermore, a pilot-scale experiment on the catalytic ozonation of bio-treated coking wastewater was carried out using an Fe-Mn-Cu-Ce/Al₂O₃ catalyst, while the effects of the initial pollutant concentration, ozone concentration, and gas flow on the COD removal rate were studied on a pilot scale. It was found that the COD removal rate of the wastewater was ～ 60 % under optimal parameters. After the treatment, the wastewater steadily reached the coking wastewater discharge standard (COD < 80 mg/L), while the operating cost of catalytic ozonation reached ～ 0.032$/m³, thereby paving the way toward economic engineering applications. The COD degradation kinetics in the bio-treated coking wastewater followed pseudo-second-order kinetics. Three-dimensional fluorescence and gas chromatography–mass spectrometry revealed that macromolecular organic pollutants in the bio-treated coking wastewater were greatly degraded. In summary, Fe-Mn-Cu-Ce/Al₂O₃ exhibited good reusability, high catalytic activity, and low cost and has a wide application prospect in the treatment of coking wastewater.     

α‐FeOOH−MoO3 Nanorod for Effective Photo‐Fenton Degradation of Dyes and Antibiotics at a Wide Range of pH

It's highly significant to develop a novel catalyst, which can be active at a wide range of pH, for an effective photo‐Fenton reaction. In this work, α‐FeOOH?MoO₃ nanorod was prepared by a one‐step hydrothermal method and applied in photo‐Fenton degradation of organic pollutants. Benefit from the electron migration mechanism of Z‐scheme and excellent photoelectric performance, the catalyst exhibited superior photo‐Fenton activity in degradation of organic pollutants. In addition, the catalyst holds good stability after 5 recycles. These results demonstrated that this catalyst has wide application prospect in organic wastewater treatment.     

过硫酸盐活化高级氧化新技术

过硫酸盐在热、光、过渡金属催化等条件激活下产生强氧化性的硫酸根自由基·SO₄^-。基于·SO₄^-的过硫酸盐活化“高级氧化技术”在环境污染治理领域的应用,是刚刚发展起来的崭新的研究方向,具有广阔的应用前景。本文在分析其基本原理的基础上,综述了过硫酸盐活化技术在国内外土壤地下水有机污染原位修复、难降解有机废水处理等环境污染治理方面的研究进展,并就存在问题进行了研究展望。     

Improving piezoelectric performance of lead-free polymer composites with high aspect ratio BaTiO3 nanowires

Flexible and lead-free piezoelectric nanocomposites were synthesized with BaTiO₃ nanowires (filler) and poly(vinylidene fluoride) (PVDF) (matrix), and the piezoelectric performances of the composites were systematically studied by varying the aspect ratio (AR) and volume fraction of the nanowire and poling time. BaTiO₃ nanowires with AR of 18 were synthesized and incorporated into PVDF to improve the piezoelectric performance of the composites. It was found that high AR significantly increased the dielectric constant up to 64, which is over 800% improvement compared to those from the composites containing spheroid shape BaTiO₃ nanoparticles. In addition, the dielectric constant and piezoelectric coefficient were also enhanced by increasing the concentration of BaTiO₃ nanowires. The piezoelectric coefficient with 50-vol% BaTiO₃ nanowires embedded in PVDF displayed 61 pC/N, which is much higher than nanocomposites with spheroid shape BaTiO₃ nanoparticles as well as comparable to, if not better, other nanoparticle-filled polymer composites. Our results suggest that it is possible to fabricate nanocomposites with proper mechanical and piezoelectric properties by utilizing proper AR fillers.     

Nano‐Ferroelectric for High Efficiency Overall Water Splitting under Ultrasonic Vibration

Piezocatalysis, converting mechanical vibration into chemical energy, has emerged as a promising candidate for water‐splitting technology. However, the efficiency of the hydrogen production is quite limited. We herein report well‐defined 10 nm BaTiO₃ nanoparticles (NPs) characterized by a large electro‐mechanical coefficient which induces a high piezoelectric effect. Atomic‐resolution high angle annular dark field scanning transmission electron microscopy (HAADF‐STEM) and scanning probe microscopy (SPM) suggests that piezoelectric BaTiO₃ NPs display a coexistence of multiple phases with low energy barriers and polarization anisotropy which results in a high electro‐mechanical coefficient. Landau free energy modeling also confirms that the greatly reduced polarization anisotropy facilitates polarization rotation. Employing the high piezoelectric properties of BaTiO₃ NPs, we demonstrate an overall water‐splitting process with the highest hydrogen production efficiency hitherto reported, with a H₂ production rate of 655 μmol g^?1 h^?1, which could rival excellent photocatalysis system. This study highlights the potential of piezoelectric catalysis for overall water splitting.     

Mechanically Activated Solid-State Radical Polymerization and Cross-Linking via Piezocatalysis

Piezocatalysis offers a means to transduce mechanical energy into chemical potential, harnessing physical force to drive redox reactions. Working in the solid state, we show here that piezoelectric BaTiO₃ nanoparticles can transduce mechanical load into a flux of reactive radical species capable of initiating solid state free radical polymerization. Activation of a BaTiO₃ powder by ball milling, striking with a hammer, or repeated compressive loading generates highly reactive hydroxyl radicals (⋅OH), which readily initiate radical chain growth and crosslinking of solid acrylamide, acrylate, methacrylate and styrenic monomers. Control experiments indicate a critical role for chemisorbed water on the BaTiO₃ nanoparticle surface, which is oxidized to ⋅OH via mechanoredox catalysis. The force-induced production of radicals by compressing dry piezoelectric materials represents a promising new route to harness mechanical energy for solid state radical synthesis.     

Highly dispersed Mn2O3−Co3O4 nanostructures on carbon matrix as heterogeneous Fenton-like catalyst

This work reports the synthesis of various carbon (Vulcan XC-72 R) supported metal oxide nanostructures, such as Mn₂O₃, Co₃O₄ and Mn₂O₃−Co₃O₄ as heterogeneous Fenton-like catalysts for the degradation of organic dye pollutants, namely Rhodamine B (RB) and Congo Red (CR) in wastewater. The activity results showed that the bimetallic Mn₂O₃−Co₃O₄/C catalyst exhibits much higher activity than the monometallic Mn₂O₃/C and Co₃O₄/C catalysts for the degradation of both RB and CR pollutants, due to the synergistic properties induced by the Mn−Co and/or Mn (Co)−support interactions. The degradation efficiency of RB and CR was considerably increased with an increase of reaction temperature from 25 to 45°C. Importantly, the bimetallic Mn₂O₃−Co₃O₄/C catalyst could maintain its catalytic activity up to five successive cycles, revealing its catalytic durability for wastewater purification. The structure–activity correlations demonstrated a probable mechanism for the degradation of organic dye pollutants in wastewater, involving •OH radical as well as Mn²⁺/Mn³⁺ or Co²⁺/Co³⁺ redox couple of the Mn₂O₃−Co₃O₄/C catalyst.     

CuFe2O4@GO nanocomposite as an effective and recoverable catalyst of peroxymonosulfate activation for degradation of aqueous dye pollutants

Recently, heterogeneous activation of peroxymonosulfate (PMS) to oxidatively degrade organic pollutants has been a hotspot. In the present work, copper ferrite-graphite oxide hybrid (CuFe₂O₄@GO) was prepared and used as catalyst to activate PMS for degradation of methylene blue (MB) in aqueous solution. A high degradation efficiency (93.3%) was achieved at the experimental conditions of 20 mg/L MB, 200 mg/L CuFe₂O₄@GO, 0.8 mmol/L PMS, and 25 °C temperature. Moreover, CuFe₂O₄@GO showed an excellent reusability and stability. The effects of various operational parameters including pollutant type, solution pH, catalyst dosage, PMS dosage, pollutant concentration, temperature, natural organic matter (NOM), and inorganic anions on the catalytic degradation process were comprehensively investigated and elucidated. The further mechanistic study revealed the Cu(II)/Cu(I) redox couple on CuFe₂O₄@GO played the dominant role in PMS activation, where both hydroxyl and sulfate radicals were generated and proceeded the degradation of pollutants. In general, CuFe₂O₄@GO is a promising heterocatalyst for PMS-based advanced oxidation processes (AOPs) in wastewater treatment.     

The electrochemical advanced oxidation processes coupling of oxidants for organic pollutants degradation: A mini-review

The electrochemical advanced oxidation processes(EAOPs) have been extensively applied in the treatment of organic pollutants degradation.Herein,the mini review provides the coupling systems about EAOPs and different oxidants(e.g.,persulfate(PS),peroxymonosulfate(PMS),and ozone(O_3)),including EAOPs-PS systems,EAOPs-PMS systems,EAOPs-peroxone systems,and photoelectro-oxidants systems,for the organic compounds degradation.The coupling system of EAOPs with oxidants is an effective way to improve the generated free radicals(e.g.,HO~·and SO_4~(·-)) concentration and to accelerate pollutant degradation.In this review,we make a summary of the homogeneous and heterogeneous EAOPs-oxidant processes.The reaction mechanisms of EAOPs combined with different oxidants are elucidated in detail,as well as the synergistic effect for improving the degradation and mineralization efficiency.     

Flower-like shaped Bi12TiO20/g-C3N4 heterojunction for effective elimination of organic pollutants: Preparation,characterization, and mechanism study

Flower-like shaped Bi₁₂TiO₂₀ (Bismuth Titanate)/g-C₃N₄ (graphite-like carbon nitride) heterojunction was prepared through hydrothermal and sonification methods for the degradation of organic pollutants by visible-light irradiation. The preparation process, chemical structures, and the mechanism of photocatalytic enhancement of the heterostructures were studied systematically. Under visible-light irradiation, the novel flower-like shaped Bi₁₂TiO₂₀/g-C₃N₄ heterojunction demonstrates prominent activities for the degradation of rhodamine B and p-nitrophenol, with the introduction of flower-like shaped Bi₁₂TiO₂₀ into g-C₃N₄ composites greatly increasing the activity of pure g-C₃N₄. This activity enhancement for the heterojunction could be mainly attributed to its low recombination speed of electron–hole pairs, high adsorption ability of organic pollutants, and better optical absorption ability. Moreover, in the visible-light system of Bi₁₂TiO₂₀/g-C₃N₄, ^•OH also contributed to the degradation of pollutants, which may explain the enhanced photocatalytic activity after the introduction of Bi₁₂TiO_20, as ^•OH is inactive in pure g-C₃N₄. Furthermore, 10 wt.% Bi₁₂TiO₂₀/g-C₃N₄ showed not only high activity but also good stability for degradation of aqueous organic pollutants, implying potential applications prospect.     

Surfactant Assisted Hydrothermal Synthesis of Superparamagnetic ZnFe<Subscript>2</Subscript>O<Subscript>4</Subscript> Nanoparticles as an Efficient Visible-Light Photocatalyst for the Degradation of Organic Pollutant

Super paramagnetic ZnFe₂O₄ nanoparticles were prepared by a surfactant assisted (ethylamine) hydrothermal method along with heat treatment. The nanoparticles were characterized by X-ray diffraction, Fourier transform infrared spectroscopy, high resolution scanning electron microscopy, Transmission electron microscopy, vibrating sample magnetometer and diffuse reflectance spectra technique. From the analyses, influence of calcination temperature on the structural, vibrational, morphological, magnetic and optical properties of ZnFe₂O₄ nanoparticles were investigated. The ZnFe₂O₄ nanoparticles with an average particle size of 17 nm showed high photocatalytic activity in the degradation of methylene blue (90 %). This work demonstrates that ZnFe₂O4 can be used as a potential monocomponent in visible-light photocatalysis for the degradation of organic pollutants. Furthermore, the products were super paramagnetic and could be conveniently separated within 15 min and recycled by using simple magnet, which is very beneficial for the degradation of organic pollutants.     

Mechanochemically sulfured FeS1.92 as stable and efficient heterogeneous Fenton catalyst

Fenton reaction is one of most promising approaches for efficient removal of various robust organic pollutants in wastewater, however it faces several intrinsic challenges such as acidic condition, sludge waste and sensitive to sulfide-containing compound. Here we reported a novel FeS_1.92 as an efficient and sulfide resistant heterogeneous Fenton catalyst under mild condition. This novel FeS_1.92 was facilely prepared through a mechanochemical synthesis of mackinawite (FeS) with sulfur powder (S) by ball milling. The sulfured mackinawite (FeS_1.92) exhibits high performance in activating H₂O₂ to generate hydroxyle radicals for organic waste remediation. Furthermore, this FeS_1.92 based heterogeneous Fenton catalyst is highly sulfide resistant and shows improved performance for degrading sulfide-containing organic pollutants. This study provides an effective mechanochemical approach to fabricate heterogeneous Fenton catalysts for sulfide-containing wastewater treatment.     

The carbon nanotubes-based materials and their applications for organic pollutant removal:A critical review

The carbon nanotubes(CNTs) as the emerging materials for organic pollutant removal have gradually become a burgeoning research field.Herein,a mini-review of CNTs-based materials curre ntly studies for organic pollutant elimination is presented.This review summarizes the preparation methods of CNTsbased materials.CNTs-based materials can be used as adsorbents to remove organic pollutants in wastewater.The adsorption mechanisms mainly include surface diffusio n,pore diffusion and adsorption reaction.Most importantly,an in-depth overview of CNTs-based materials currently available in advanced oxidation processes(AOPs) applications for wastewater treatment is proposed.CNTs-based materials can catalyze different oxidants(e.g.,hydrogen peroxide(H_2 O_2),persulfates(PMS/PDS),ozone(O_3) and ferrate/permanganate(Fe(Ⅵ)/Mn(Ⅶ)) to generate more reactive oxygen species(ROS) for organic pollutant elimination.Moreover,the possible reaction mechanisms of removing organic pollutants by CNTs-based materials are summarized systematically and discussed in detail.Finally,application potential and future research directions of CNTs-based materials in the environmental remediation field are proposed.     

Heterojunction architecture of Nb2O5/g-C3N4 for enhancing photocatalytic activity to degrade organic pollutants and deactivate bacteria in water

Water pollution has become a serious problem owing to the development of society. Photocatalysis is a promising approach to remove various pollutants in water, such as organic pollutants and antibiotic resistance bacteria. Meanwhile, the design of heterojunction between two semiconductors is an effective path to improve photocatalytic properties due to its potential in improving separation and transfer of photoinduced carriers. In this study, Nb₂O₅/g-C₃N₄ (NO/CN) composite materials were prepared through a one-step heating method. Characterizations confirmed successful preparation of NO/CN heterojunction structure and better optical properties than pure g-C₃N₄ and Nb₂O₅. NO/CN composite materials showed excellent photocatalytic efficiency for Escherichia coli (E. coli) inactivation (95%) compared with the pure Nb₂O₅ (10%) and g-C₃N₄ (77%). Meanwhile, NO/CN exhibited better organic pollutants removal (RhB for 94%, methyl orange (MO) for 15% and methylene blue (MB) for 87%) under visible light, which is likely owing to the heterojunction structure between g-C₃N₄ and Nb₂O₅ that leads to the good separation of photogenerated electron-hole pair. Free radical scavenging and electron spin resonance (ESR) experiments demonstrated that superoxide radicals (^?O₂^?) and holes (h⁺) were the dominant radicals. Therefore, the NO/CN was proposed to be a promising material for effective disinfection and removal of organic contaminants in water treatment.     

Designing 3D-MoS2 Sponge as Excellent Cocatalysts in Advanced Oxidation Processes for Pollutant Control

3D-MoS₂ can adsorb organic molecules and provide multidimensional electron transport pathways, implying a potential application for environment remediation. Here, we study the degradation of aromatic organics in advanced oxidation processes (AOPs) by a 3D-MoS₂ sponge loaded with MoS₂ nanospheres and graphene oxide (GO). Exposed Mo⁴⁺ active sites on 3D-MoS₂ can significantly improve the concentration and stability of Fe²⁺ in AOPs and keep the Fe³⁺/Fe²⁺ in a stable dynamic cycle, thus effectively promoting the activation of H₂O₂/peroxymonosulfate (PMS). The degradation rate of organic pollutants in the 3D-MoS₂ system is about 50 times higher than without cocatalyst. After a 140 L pilot-scale experiment, it still maintains high efficiency and stable AOPs activity. After 16 days of continuous reaction, the 3D-MoS₂ achieves a degradation rate of 120 mg L⁻¹ antibiotic wastewater up to 97.87 %. The operating cost of treating a ton of wastewater is only US$ 0.33, suggesting huge industrial applications.     

Built-in piezoelectric field improved photocatalytic performance of nanoflower-like Bi2WO6 using low-power white LEDs

Photocatalysis technology has been proved to be a potential strategy for removal of organic dyes, however high-power light sources are generally necessary to initiate photocatalytic reaction. In this work, we employed an excellent photocatalyst of Bi₂WO₆ with visible light harvest and meanwhile an intrinsic ferroelectricity, which realized the efficient degradation of organic dye via the synergetic photopiezocatalysis. Through coupling the illumination by a low-power (9 W) LED and the ultrasonic vibration (120 W) by an ultrasonic cleaner, the nanoflower-like Bi₂WO₆ composed of ultrathin nanosheets showed a much more enhanced photopiezocatalysis performance for purification of organic dye than the individual photocatalysis and piezocatalysis. Furthermore, the high mineralization efficiency and the good durability of the Bi₂WO₆ catalyst were demonstrated. The possible mechanism of photopiezocatalysis was finally proposed, where the ultrasound-induced piezoelectric field in Bi₂WO₆ drove photo-generated electrons and holes to diffuse along opposite directions, consequently promoting the separation efficiency of charge carriers. This work indicates that the synergetic photopiezocatalysis by coupling irradiation and ultrasonic vibration is a promising strategy to purify organic pollutants in wastewater.     

Recent advances in persulfate-based advanced oxidation processes for organic wastewater treatment

In recent years, with the emergence of new pollutants, the effective treatment of wastewater has become very important. Persulfate-based advanced oxidation processes have been successfully applied to the treatment of wastewater, such as wastewater containing antibiotics, pharmaceuticals and personal care products, dyes, endocrine-disrupting chemicals, chlorinated organic pollutants, and phenolics, for the degradation of refractory organic contaminants. This paper summarizes the production of sulfate radicals, which can be generated by the activation of persulfate via conventional and emerging approaches. The existing problems of persulfate-based advanced oxidation processes were analyzed in detail, including residual sulfates, coexisting factors (coexisting inorganic anions and natural organic matter), and energy consumption. This paper proposes corresponding possible solutions to the problems mentioned above, and this paper could provide a reference for the application of persulfate-based advanced oxidation processes in actual wastewater treatment.     

CoFe2O4 with MoS2-xOy Nanosheets as a Co-catalyst for Enhanced Activation of Peroxydisulfate in Advanced Oxidation Processes

The application of advanced oxidation processes (AOPs) based on sulfate radicals for degrading persistent organic pollutants faces challenges due to the inefficient activation of peroxydisulfate (PDS) oxidant. Herein, a composite CoFe₂O₄/MoS_2-xO_y (CFM) catalyst consisting of CoFe₂O₄ nanoparticles uniformly dispersed on the nanosheets of oxygen-incorporated MoS₂ (MoS_2-xO_y) with flower-like morphology are fabricated through a facile two-step hydrothermal method, which results in the enhanced activation of PDS and a highly efficient degradation of phenolic pollutants. The oxygen-doping in MoS_2-xO_y leads to unsaturated sulfur and active sites on the surface of MoS₂ for accelerating the rate limiting step of Fe^III/Fe^II reduction cycle in PDS-CFM reaction. Aiming at the refractory organic pollutants in actual coking wastewater, CFM co-catalyst is introduced into a hydrogel made up of polyvinyl alcohol (PVA) and coal-tar pitch oxides (PO) to construct a multifunctional CFM@PO/PVA hydrogel. Upon hybrid CFM@PO/PVA, the coupling of the enhanced AOP with solar-driven interfacial vapor generation (SIVG) technology contributes to the degradation efficiency, the removal rate of phenol in solution and the total organic carbon in coking wastewater can reach 98 % and 91 %, respectively. The integration of heterogeneous AOPs with SIVG system provides a feasible strategy for the eco-friendly efficient purification of industrial wastewater.     

Designing 3D‐MoS2 Sponge as Excellent Cocatalysts in Advanced Oxidation Processes for Pollutant Control

3D‐MoS₂ can adsorb organic molecules and provide multidimensional electron transport pathways, implying a potential application for environment remediation. Here, we study the degradation of aromatic organics in advanced oxidation processes (AOPs) by a 3D‐MoS₂ sponge loaded with MoS₂ nanospheres and graphene oxide (GO). Exposed Mo⁴⁺ active sites on 3D‐MoS₂ can significantly improve the concentration and stability of Fe²⁺ in AOPs and keep the Fe³⁺/Fe²⁺ in a stable dynamic cycle, thus effectively promoting the activation of H₂O₂/peroxymonosulfate (PMS). The degradation rate of organic pollutants in the 3D‐MoS₂ system is about 50 times higher than without cocatalyst. After a 140 L pilot‐scale experiment, it still maintains high efficiency and stable AOPs activity. After 16 days of continuous reaction, the 3D‐MoS₂ achieves a degradation rate of 120 mg L^?1 antibiotic wastewater up to 97.87 %. The operating cost of treating a ton of wastewater is only US$ 0.33, suggesting huge industrial applications.