Magnetic pyrite cinder as an efficient heterogeneous ozonation catalyst and synergetic effect of deposited Ce

Effect of temperature on the reaction path of pyrite (FeS2)-based catalyst catalyzed CO reduction of SO2 to sulfur

To understand the physical phase structural variation and activation pathway of the active component during the catalytic reduction of pyrite (FeS2)-based catalysts, multiple methods, including X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), and high-temperature in situ XRD, were applied to characterize the catalyst and reaction process. The reaction mechanism was simulated and verified using density functional theory. The results indicated that pyrite-based catalysts promote the CO reduction of SO2 to S through the dynamic transformation of three phases (FeS2, Fe7S8, and FeS), in which S-vacancy formation is the most important step. As the critical temperature for the reaction of FeS2 and CO was initiated at approximately 525 °C, the active component's physical phase structure and activation pathway could be controlled by adjusting the temperature.

State of Art and Perspectives in Catalytic Ozonation for Removal of Organic Pollutants in Water: Influence of Process and Operational Parameters

The number of organic pollutants detected in water and wastewater is continuously increasing thus causing additional concerns about their impact on public and environmental health. Therefore, catalytic processes have gained interest as they can produce radicals able to degrade recalcitrant micropollutants. Specifically, catalytic ozonation has received considerable attention due to its ability to achieve advanced treatment performances at reduced ozone doses. This study surveys and summarizes the application of catalytic ozonation in water and wastewater treatment, paying attention to both homogeneous and heterogeneous catalysts. This review integrates bibliometric analysis using VOS viewer with systematic paper reviews, to obtain detailed summary tables where process and operational parameters relevant to catalytic ozonation are reported. New insights emerging from heterogeneous and homogenous catalytic ozonation applied to water and wastewater treatment for the removal of organic pollutants in water have emerged and are discussed in this paper. Finally, the activities of a variety of heterogeneous catalysts have been assessed using their chemical–physical parameters such as point of zero charge (PZC), pKa, and pH, which can determine the effect of the catalysts (positive or negative) on catalytic ozonation processes.

Pyrite-mediated advanced oxidation processes: Applications, mechanisms, and enhancing strategies

Proper treatment of wastewater is one of the key issues to the sustainable development of human society, and people have been searching for high-efficiency and low-cost methods for wastewater treatment. This article reviews recent studies about pyrite-mediated advanced oxidation processes (AOPs) in removing refractory organics from wastewater. The basic information of pyrite and its characteristics for AOPs are first introduced. Then, the performance and mechanisms of pyrite-mediated Fenton oxidation, electro-Fenton oxidation, and persulfate oxidation processes are carefully reviewed and presented. Natural pyrite is an abundant low-cost heterogeneous catalyst for AOPs, and the slow release of Fe²⁺ and the self-regulation of solution pH are highlighted characteristics of pyrite-mediated AOPs. In AOPs, the interaction between Fe³⁺ and pyrite facilitates the Fe²⁺ regeneration and the Fe²⁺/Fe³⁺ cycle. Making pyrite into nanoparticles, assisting by ultrasound and light irradiation, and adding exogenous Fe³⁺, organic chelating agents, or biochar is effective to enhance the performance of pyrite-mediated AOPs. Based on the analyses of those pyrite-mediated AOPs and their enhancing strategies, the future development directions are proposed in the aspects of toxicity research, mechanism research, and technological coupling.

Enhanced degradation of dimethyl phthalate in wastewater via heterogeneous catalytic ozonation process: performances and mechanisms

Ozonation process is a promising yet challenging method for the removal of refractory organic matter due to the sluggish reaction for generating hydroxyl radical (˙OH) at a neutral pH condition. Herein, an efficient heterogeneous catalytic ozonation system using CeO₂/Al₂O₃ catalyst was developed to remove dimethyl phthalate (DMP) from wastewater. Under a neutral condition of pH = 6, this system achieved almost 100% DMP removal within 15 min at an optimized catalyst dosage of 30 g L⁻¹ and the ozone flow rate of 22.5 mg min⁻¹. Moreover, the catalytic ozonation system exhibited a stable degradation performance of DMP in a wider pH range (pH = 5–10). The results of electron paramagnetic resonance (EPR) and quantitative tests confirmed the ultrafast conversion of O₃ to ˙OH (0.774 μM min⁻¹) on the surface of CeO₂ based ceramic catalyst. The quenching experiments further supported the predominant role of ˙OH in the mineralization of DMP. These results highlight the potential of using the heterogeneous catalytic ozonation system for the efficient removal of refractory organic matter from wastewater.

An efficient heterogeneous catalytic ozonation system using CeO₂/Al₂O₃ catalyst was developed to remove dimethyl phthalate (DMP) from wastewater.

Reactive Oxygen Species and Catalytic Active Sites in Heterogeneous Catalytic Ozonation for Water Purification

Heterogeneous catalytic ozonation (HCO) processes have been widely studied for water purification. The reaction mechanisms of these processes are very complicated because of the simultaneous involvement of gas, solid, and liquid phases. Although typical reaction mechanisms have been established for HCO, some of them are only appropriate for specific systems. The divergence and deficiency in mechanisms hinders the development of novel active catalysts. This critical review compares the various existing mechanisms and categorizes the catalytic oxidation of HCO into radical-based oxidation and nonradical oxidation processes with an in-depth discussion. The catalytic active sites and adsorption behaviors of O₃ molecules on the catalyst surface are regarded as the key clues for further elucidating the O₃ activation processes, evolution of reactive oxygen species (ROS) or organic oxidation pathways. Moreover, the detection methods of the ROS produced in both types of oxidations and their roles in the destruction of organics are reviewed with discussion of some specific problems among them, including the scavengers selection, experiment results analysis as well as some questionable conclusions. Finally, alternative strategies for the systematic investigation of the HCO mechanism and the prospects for future studies are envisaged.

Pharmaceutically active compounds in aqueous environment: A status, toxicity and insights of remediation

Pharmaceutically active compounds (PhACs) have pernicious effects on all kinds of life forms because of their toxicological effects and are found profoundly in various wastewater treatment plant influents, hospital effluents, and surface waters. The concentrations of different pharmaceuticals were found in alarmingly high concentrations in various parts of the globe, and it was also observed that the concentration of PhACs present in the water could be eventually related to the socio-economic conditions and climate of the region. Drinking water equivalent limit for each PhAC has been calculated and compared with the occurrence data from various continents. Since these compounds are recalcitrant towards conventional treatment methods, while advanced oxidation processes (AOPs) have shown better efficiency in degrading these PhACs. The performance of the AOPs have been evaluated based on percentage removal, time, and electrical energy consumed to degrade different classes of PhACs. Ozone based AOPs were found to be favorable because of their low treatment time, low cost, and high efficiency. However, complete degradation cannot be achieved by these processes, and various transformation products are formed, which may be more toxic than the parent compounds. The various transformation products formed from various PhACs during treatment have been highlighted. Significant stress has been given on the role of various process parameters, water matrix, oxidizing radicals, and the mechanism of degradation. Presence of organic compounds, nitrate, and phosphate usually hinders the degradation process, while chlorine and sulfate showed a positive effect. The role of individual oxidizing radicals, interfering ions, and pH demonstrated dissimilar effects on different groups of PhACs.

Continuous-flow ozonation over modified ceramsite: implications for the degradation of cation red x-GRL

Catalytic ozonation has been widely used for refractory dye wastewater treatment due to highly reactive HO·. In this study, a kind of low-cost and environmental-friendly modified ceramsite sphere derived from pyrite cinder, silty clay and kaolin was prepared as ozonation catalyst. The degradation performances of cation red x-GRL were performed under a continuous mode. Being close to the practical treatment, continuous-flow ozonation study is vital for applying heterogeneous catalytic ozonation in wastewater treatment at a large industrial scale. Results showed that the absorption capacity of this modified ceramsite towards cation red x-GRL was confirmed to be slight. The mineralization efficiency was high, accounting for 48.0% of 200 mg/L cation red x-GRL at a constant flow rate of 0.18 L/min (hydraulic retention time = 16 min), while only 7.8% during ozonation alone. Furthermore, this novel catalytic ozonation can maintain high mineralization efficiency in a wide range of pH (3-10), which was ascribed to the synergistic catalytic performance of various oxides. The reaction mechanism is ascribed to the promotion of ·OH production from O₃ molecules' decomposition. Moreover, ozone utilization efficiency at hydraulic retention time of 16 min during catalytic ozonation was 2.0 times as high as that during ozonation alone.

Evaluation of advanced oxidation processes for water and wastewater treatment - A critical review

This study provides an overview of established processes as well as recent progress in emerging technologies for advanced oxidation processes (AOPs). In addition to a discussion of major reaction mechanisms and formation of by-products, data on energy efficiency were collected in an extensive analysis of studies reported in the peer-reviewed literature enabling a critical comparison of various established and emerging AOPs based on electrical energy per order (E_EO) values. Despite strong variations within reviewed E_EO values, significant differences could be observed between three groups of AOPs: (1) O₃ (often considered as AOP-like process), O₃/H₂O₂, O₃/UV, UV/H₂O₂, UV/persulfate, UV/chlorine, and electron beam represent median E_EO values of <1 kWh/m³, while median energy consumption by (2) photo-Fenton, plasma, and electrolytic AOPs were significantly higher (E_EO values in the range of 1-100 kWh/m³). (3) UV-based photocatalysis, ultrasound, and microwave-based AOPs are characterized by median values of >100 kWh/m³ and were therefore considered as not (yet) energy efficient AOPs. Specific evaluation of 147 data points for the UV/H₂O₂ process revealed strong effects of operational conditions on reported E_EO values. Besides water type and quality, a major influence was observed for process capacity (lab-vs. pilot-vs. full-scale applications) and, in case of UV-based processes, of the lamp type. However, due to the contribution of other factors, correlation of E_EO values with specific water quality parameters such as UV absorbance and dissolved organic carbon were not substantial. Also, correlations between E_EO and compound reactivity with OH-radicals were not significant (photolytically active compounds were not considered). Based on these findings, recommendations regarding the use of the E_EO concept, including the upscaling of laboratory results, were derived.

Ozonation of dimethyl phthalate catalyzed by highly active CuxO-Fe3O4 nanoparticles prepared with zero-valent iron as the innovative precursor

Heterogeneous catalytic ozonation provides a promising alternative in the degradation of recalcitrant contaminants. Cu_xO-Fe₃O₄ nanoparticles (Cu_xFeO NPs, both Cu(I) and Cu(II) were contained, about 70 nm) were creatively synthesized using Fe(0) as the precursor and subsequently employed as the ozonation catalyst for dimethyl phthalate (DMP) degradation. Results showed that DMP degradation by O₃/Cu_xFeO was significantly faster than those ozonation catalyzed by CuO, Fe₃O₄, or mixture of CuO and Fe₃O₄ (1:1 M ratio), which was ascribed to the unique Cu_xFeO NPs that composed of abundant structural Cu(I) (≡Cu(I)). It was among the first revealing the synergistic effect between ≡Cu(I) and surface lattice oxygen (O^2-) in HO· generation, resulting in rapid DMP degradation kinetics and high mineralization efficiency. Besides the generation of ≡Cu(I), galvanic corrosion between Fe(0) and Cu(II) also generated structural Fe(II), which could reduce the ≡Cu(II) back to ≡Cu(I), thus compensating the electron loss of ≡Cu(I) and finally obtaining a high-efficiency cycling between ≡Cu(II) and ≡Cu(I). The DMP degradation pathway was introduced based on the intermediates detected. By regulating the (re)-generation of low-valent metal (≡Cu(I)), this study provides an innovative strategy to significantly promote the generation of HO· in catalytic ozonation, which might be promising for advanced wastewater treatment.

Pretreatment of shale gas drilling flowback fluid (SGDF) by the microscale Fe0/persulfate/O3 process (mFe0/PS/O3)

Shale gas drilling flowback fluid (SGDF) generated during shale gas extraction is of great concern due to its high total dissolved solid, radioactive elements and organic matter. To remove the toxic and refractory pollutants in SGDF and improve its biodegradability, a microsacle Fe⁰/Persulfate/O₃ process (mFe⁰/PS/O₃) was developed to pretreat this wastewater obtained from a shale gas well in southwestern China. First, effects of mFe⁰ dosage, O₃ flow rate, PS dosage, pH values on the treatment efficiency of mFe⁰/PS/O₃ process were investigated through single-factor experiments. Afterward, the optimal conditions (i.e., pH = 6.7, mFe⁰ dosage = 6.74 g/L, PS = 16.89 mmol/L, O₃ flow rate = 0.73 L/min) were obtained by using response surface methodology (RSM). Under the optimal conditions, high COD removal (75.3%) and BOD₅/COD ratio (0.49) were obtained after 120 min treatment. Moreover, compared with control experiments (i.e., mFe⁰, O₃, PS, mFe⁰/O₃, mFe⁰/PS, O₃/PS), mFe⁰/PS/O₃ system exerted better performance for pollutants removal in SGDF due to strong synergistic effect between mFe⁰, PS and O₃. In addition, the decomposition or transformation of the organic pollutants in SGDF was analyzed by using GC-MS. Finally, the reaction mechanism of the mFe⁰/PS/O₃ process was proposed according to the analysis results of SEM-EDS and XRD. It can be concluded that high-efficient mFe⁰/PS/O₃ process was mainly resulted from the combination effect of direct oxidation by ozone and persulfate, heterogeneous and homogeneous catalytic oxidation, Fenton-like reaction and adsorption. Therefore, mFe⁰/PS/O₃ process was proven to be an effective method for pretreatment of SGDF prior to biological treatment.

Production of pyrite nanoparticles using high energy planetary ball milling for sonocatalytic degradation of sulfasalazine

Sonocatalytic performance of pyrite nanoparticles was evaluated by the degradation of sulfasalazine (SSZ). Pyrite nanoparticles were produced via a high energy mechanical ball milling (MBM) in different processing time from 2h to 6h, in the constant milling speed of 320rpm. X-ray diffraction (XRD), scanning electron microscopy (SEM) coupled with energy dispersive X-ray (EDX), Fourier transform infrared spectroscopy (FT-IR) analysis and Brunauer-Emmett-Teller (BET) confirmed the production of pyrite nanoparticles during 6h of ball milling with the average size distribution of 20-80nm. The effects of various operational parameters including pH value, catalyst amount (mg/L), SSZ concentration (mg/L), ultrasonic frequency (kHz) and reaction time on the SSZ removal efficiency were examined. The obtained results showed that the maximum removal efficiency of 97.00% was obtained at pH value of 4, catalyst dosage of 0.5g/L, SSZ concentration of 10mg/L and reaction time of 30min. Experimental results demonstrated that the kinetic of the degradation process can be demonstrated using Langmuir-Hinshelwood (L-H) kinetic model. The effect of different inorganic ions such as Cl^-, CO₃^2- and SO₄^2- was investigated on the L-H reaction rate (k_r) and adsorption (K_s) constants. Results showed that the presence of the mentioned ions significantly influenced the L-H constants. The impact of ethanol as a OH radical scavenger and some enhancers including H₂O₂ and K₂S₂O₈ was investigated on the SSZ removal efficiency. Accordingly, the presence of ethanol suppressed SSZ degradation due to the quenching of OH radicals and the addition of K₂S₂O₈ and H₂O₂ increased the SSZ removal efficiency, due to the formation of SO₄^- and additional OH radicals, respectively. Under the identical conditions of operating parameters, pyrite nanoparticles maintained their catalytic activity during four consecutive runs.