Catalytic Advanced Oxidation Processes Research Articles

Improving Generation Performance of 1O2 by Atomic Doping for Efficient Catalytic Advanced Oxidation Processes

AbstractSinglet oxygen (1O2) has attracted great attention owing to its superior comprehensive oxidizing performance and extensive application in dealing with ever‐growing environmental pollution. However, the efficient catalytic generation of 1O2 is very challenging due to the low catalytic activity of most catalysts and the generation of oxygen‐containing radicals in the catalytic reaction. Herein, C‐doped Co nanoparticles (CoNPs) supported on porous carbon (C─Co/C) as highly reactive and selective 1O2‐producing catalysts are demonstrated for efficient catalytic oxidation of recalcitrant organics via activation of peroxymonosulfate (PMS). The doped C 2p orbitals can accept Co 3d electrons, thereby weakening the Co─O bonding between Co and PMS or other oxygen‐containing intermediates such as *SO4, *OH, *OOH, and *O. The adsorption and cleavage energy of PMS on Co nanoparticle is reduced from 8.09 to 4.64 eV by C doping. The energy barrier of the *OOH to 1O2 step is also lowered significantly, thereby kinetically improving the activity for the generation of 1O2. The C─Co/C catalysts promotes the efficient and 100% selective generation of 1O2 with high modified kinetic model (K) values of 457.0 and 94.5 µmol s−1 g−1 for rhodamine (RhB) and 2,4‐dichlorophenol (2,4‐DCP), respectively.

Effect of log Kow on the degradation of pharmaceutically active compounds in a heterogeneous catalytic persulfate activation system

In heterogeneous catalytic advanced oxidation processes (HC-AOP), enhancing the reaction rate is the biggest challenge. To enhance the reaction rate, it is necessary to increase the mass transfer rate of reactants toward the catalyst surface and the number of active sites that will provide better contact with the reactants and higher mass transfer. The hydrophobicity of the reactant is an important parameter that affects the transport of molecules toward solid surfaces. In this study, the effect of log Kow, an indicator of hydrophobicity, on enhancing the catalytic activity in persulfate (PS) activation for pharmaceutic compounds (PCs) degradation was investigated. For this purpose, some PCs with different log Kow were selected and their adsorption and degradation behaviors were investigated depending on the PS concentration, catalyst dosage, contact time, pH, and temperature in HC-AOP. Adsorption percentages increased significantly with increasing log Kow value. PCs with higher log Kow were completely degraded at the end of the shorter contact times in the presence of lower catalyst and PS. PCs were significantly degraded by the triple catalytic effect of AC, Fe, and temperature. The pseudo-first-order kinetic model was the best fit for the degradation reaction for all PCs. The higher apparent rate constants and lower activation energy values of the PCs belonging to high log Kow confirmed that log Kow is an effective parameter in enhancing the catalytic activity.

The Catalytic Degradation of the Inflammatory Drug Diclofenac Sodium in Water by Fe2+/Persulfate, Fe2+/Peroxymonosulfate and Fe2+/H2O2 Processes: A Comparative Analysis

Diclofenac sodium was extensively used for treating arthritis, osteoarthritis and skeletal muscular injuries, which ultimately caused troubles for aquatic organisms as well as human beings. In this study, homogeneous catalytic advanced oxidation processes, including Fe2+/persulfate, Fe2+/peroxymonosulfate and Fe2+/H2O2, were used for the degradation of diclofenac sodium in water, without using UV-C light. About 89, 82 and 54% DCF sodium was decomposed by Fe2+/persulfate, Fe2+/peroxymonosulfate and Fe2+/H2O2, respectively, in 60 min. The degradation of diclofenac sodium followed the pseudo first-order kinetics, in all cases. The degradation efficiency of diclofenac sodium was significantly affected in the presence of various anions, such as NO3−, HCO3− and SO42−. The mineralization studies revealed 62, 45 and 32% total carbon removal by Fe2+/persulfate, Fe2+/peroxymonosulfate and Fe2+/H2O2, respectively, in 60 min. In addition, the degradation byproducts of diclofenac sodium were determined by FTIR analysis. The results revealed that the Fe2+/oxidant system, particularly Fe2+/persulfate, was a promising technology for the elimination of toxic pharmaceuticals, such as diclofenac sodium, from the water environment.

Nanohybrid catalysts with porous structures for environmental remediation through photocatalytic degradation of emerging pollutants

Water supplies have been seriously challenged by new emerging pollutants, which are difficult to remove by traditional wastewater treatment. Thus, new technologies such as catalytic advanced oxidation processes have merged as suitable solutions; however, the drawbacks of typical catalysts limit their application. To overcome this issue, new materials with enhanced textural properties have been developed, showing that their porosity and chemical nature influence their potential as a catalyst. Herein, the recent progress in highly porous catalysts and their suitable deployment to effectively nano-remediate the polluted environmental matrices are reviewed in detail. First, following a brief introduction, several environmental pollutants of emerging concerns from different sectors, including pharmaceutical residues, endocrine-disrupting chemicals (EDCs), pesticides, and hazardous dyes are also introduced with relevant examples. To effectively tackle the sustainable remediation of emerging pollutants, this work also focuses on the multifunctional features of nanohybrid porous materials that act as catalysts constructs to degrade emerging pollutants. The influence of surface reactive centers, stability, bandgap energies, light absorption capacities, and pollutants adsorption capacities are also discussed. Successful examples of the employment of nanohybrid porous catalysts for the degradation of pharmaceutical pollutants, EDCs, pesticides, and hazardous dyes are summarized. Finally, some challenges faced by nanohybrid porous materials to achieve their potential application as advanced catalysts for environmental remediation have been identified and presented herein.

Prospecting carbon-based nanomaterials for the treatment and degradation of endocrine-disrupting pollutants

The presence of endocrine-disrupting chemicals (EDCs) in water resources has significant negative implications for the environment. Traditional technologies implemented for water treatment are not completely efficient for removing EDCs from water. Therefore, research on sustainable remediation has been mainly directed to novel decontamination approaches including nano-remediation. This emerging technology employs engineered nanomaterials to clean up the environment quickly, efficiently, and sustainably. Thus, nanomaterials have contributed to a wide variety of remediation techniques like adsorption, filtration, coagulation/flocculation, and so on. Among the vast diversity of decontamination technologies catalytic advanced oxidation processes (AOPs) outstand as simple, clean, and efficient alternatives. A vast diversity of catalysts has been developed demonstrating high efficiencies; however, the search for novel catalysts with enhanced performances continues. In this regard, nanomaterials used as nanocatalysts are exhibiting enhanced performances on AOPs due to their special nanostructures and larger specific surface areas. Therefore, in this review we summarize, compare, and discuss the recent advances on nanocatalysts, catalysts doped with metal-based nanomaterials, and catalysts doped with carbon-based nanomaterials on the degradation of EDCs. Finally, further research opportunities are identified and discussed to achieve the real application of nanomaterials to efficiently degrade EDCs from water resources.

Clay-Supported Metal Oxide Nanoparticles in Catalytic Advanced Oxidation Processes: A Review.

Advanced oxidation processes (AOPs) utilizing heterogeneous catalysts have attracted great attention in the last decade. The use of solid catalysts, including metal and metal oxide nanoparticle support materials, exhibited better performance compared with the use of homogeneous catalysts, which is mainly related to their stability in hostile environments and recyclability and reusability. Various solid supports have been reported to enhance the performance of metal and metal oxide catalysts for AOPs; undoubtedly, the utilization of clay as a support is the priority under consideration and has received intensive interest. This review provides up-to-date progress on the synthesis, features, and future perspectives of clay-supported metal and metal oxide for AOPs. The methods and characteristics of metal and metal oxide incorporated into the clay structure are strongly influenced by various factors in the synthesis, including the kind of clay mineral. In addition, the benefits of nanomaterials from a green chemistry perspective are key aspects for their further considerations in various applications. Special emphasis is given to the basic schemes for clay modifications and role of clay supports for the enhanced mechanism of AOPs. The scaling-up issue is suggested for being studied to further applications at industrial scale.

Catalytic advanced oxidation processes (AOPS) in water treatment by covalent organic frameworks-based materials: a review

Catalytic advanced oxidation processes (AOPS) in water treatment by covalent organic frameworks-based materials: a review

Synthesis and characterization of γ-Fe2O3 encapsulated NaY zeolites as solid adsorbent for degradation of ceftriaxone through heterogeneous catalytic advanced oxidation processes

The degradation of ceftriaxone (CTX) by heterogeneous catalytic advanced oxidation processes has been explored using γ-Fe2O3 NaY zeolites synthesized (γ-Fe2O3@NaY) in the laboratory through hydrothermal and chemical co-precipitation methods. γ-Fe2O3@NaY zeolite was characterized by scanning electron microscopy, energy-dispersive X-ray spectroscopy and X-ray diffractometer analyses. The effects of the initial concentration of CTX and catalyst, pH and hydrogen peroxide (H2O2) dose with the presence UV light on the degradation efficiency of CTX have been studied by conducting experiments in a batch reactor at room temperature. Experimental results reveal that CTX can be efficiently removed after 90 min at pH 4.0, CTX 20 mg/L, catalyst 1.17 g/L, H2O2 30 mM and presence of UV light. A kinetic and isotherm model was developed for investigation of the adsorption mechanism, and results show that model and data are in good agreement. The reusability of γ-Fe2O3@NaY was high as it degrades CTX in the presence of UV light and H2O2 even after five consecutive cycles. Also, due to having magnetic properties, this composite is easily separated from the solution by magnetism. This work indicates that bench synthesized γ-Fe2O3 NaY zeolite is a heterogeneous recoverable catalyst that can efficiently remove CTX from wastewater.

Characterisation and utilization of steel industry waste sludge as heterogeneous catalyst for the abatement of chlorinated organics by advanced oxidation processes.

Catalytic advanced oxidation processes (AOPs) utilising UV irradiation have been reported to be highly efficient for the degradation of recalcitrant compounds. The focus of present study was to evaluate the potential of steel industry waste as an alternative to homogenous iron salts often used in AOPs. Iron rich sludge from effluent treatment plant (ETP) of a steel industry was subjected to acid washing and acid washing followed by calcination before using as catalyst for the oxidative removal of chlorinated organics present in synthetic and simulated bleaching effluents. The maximum total organic carbon removals of 64% and 25% from 4-chlorophenol solution and simulated pulp bleaching effluent, respectively were observed during photo-catalytic oxidation with acid washed steel sludge at stoichiometric H2O2 dose after 2 h reaction (catalyst dose = 1 g/L, and pH = 4.4). Low iron leaching (<2%) was observed from the catalyst even in acidic conditions and it could be reused twice without significant loss of catalytic activity.

MOF-derived CoN/N-C@SiO2 yolk-shell nanoreactor with dual active sites for highly efficient catalytic advanced oxidation processes

Optimizing the structure and composition of the yolk-shell nanoreactors are one of the effective approaches to enhance their performance in heterogeneous catalysis, yet challenging. Here, we report a facile route to synthesize a highly efficient and recyclable yolk-shell CoN/N-C@SiO2 nanoreactor with dual active sites by the direct nitridation of MOF@SiO2 precursor. The CoN yolks (∼50–70 nm) as active sites were encapsulated by the hydrophilic SiO2 shells (∼30 nm), and some small dots (∼5–10 nm) was sandwiched between void spaces. In-situ formation of N-doped carbon layer not only served as active sites but also improved electron transfer. The yolk-shell nanoreactors were applied for catalytic tetracycline (TC) degradation by activation of peroxymonosulfate (PMS), and in the optimal case, it degraded >∼95% TC within 30 min in a wide pH value range of 2.02–9.94. The quenching experiments and EPR measurements further revealed that synergistic effect of the radicals and nonradical in PMS activation, O2−, OH, SO4− and 1O2 were involved in TC degradation. The improved catalytic performances could be ascribed to the following two aspects: (1) the hydrophilic SiO2 shell and the microenvironment formed by the yolk-shell structure not only enhance catalytic stability but also provide driving force to improve reaction rate (structural modulation); (2) CoN core and N doped carbon layer as dual active sites can achieve the synergistic effect of radicals and non-radicals in PMS activation (composition modulation). Moreover, possible degradation pathways of TC were proposed through the identification of intermediates using LC–MS/MS techniques. This research highlights the critical role of structure and component optimization in construction of advanced oxidation process systems and provides the possibility of utilizing MOF derivatives in the field of electrocatalysis, lithium battery and supercapacitor etc.

Inhibitory effect of natural organic matter or other background constituents on photocatalytic advanced oxidation processes: Mechanistic model development and validation

The ability of reactive oxygen species (ROS) to interact with priority pollutants is crucial for efficient water treatment by photocatalytic advanced oxidation processes (AOPs). However, background compounds in water such as natural organic matter (NOM) can significantly hinder targeted reactions and removal efficiency. This inhibition can be complex, interfering with degradation in solution and at the photocatalyst surface as well as hindering illumination efficiency and ROS production. We developed an analytical model to account for various inhibition mechanisms in catalytic AOPs, including competitive adsorption of inhibitors, scavenging of produced ROS at the surface and in solution, and the inner filtering of the excitation illumination, which combine to decrease ROS-mediated degradation. This model was validated with batch experiments using a variety of ROS producing systems (OH-generating TiO2 photocatalyst and H2O2-UV; 1O2-generating photosensitive functionalized fullerenes and rose bengal) and inhibitory compounds (NOM, tert-butyl alcohol). Competitive adsorption by NOM and ROS scavenging were the most influential inhibitory mechanisms. Overall, this model enables accurate simulation of photocatalytic AOP performance when one or more inhibitory mechanisms are at work in a wide variety of application scenarios, and underscores the need to consider the effects of background constituents on degradation efficiency.

Electrochemical oxidation of saline industrial wastewaters using boron-doped diamond anodes

Similarly to other catalytic advanced oxidation processes electro-oxidation by means of boron-doped diamond (BDD) anodes generates a very efficient oxidant media containing, among others, hydroxyl radicals. In this work BDD electro-oxidation is demonstrated to be an efficient alternative to treat a wide variety of saline industrial effluents, which main properties were as follows: TOC = 266–4479 mg/L; [N-NH 3] = 61–1150 mg/L; [Cl −] = 1996–37,645 mg/L; conductivity = 5.6–64 mS/cm. Experiments were conducted at laboratory and pilot scale. Treatment efficiency was evaluated in terms of TOC and N-NH 3 removal, and of formation of undesired by-products such as nitrate ions and trihalomethanes. The results showed that the high concentration of chloride ions in the wastewaters resulted in chloride oxidation taking place primarily, favouring ammonia oxidation in detriment of TOC elimination. Consequently, complete elimination of ammonia could be achieved for all the wastewaters studied while TOC removals reached values as high as 90%. Additionally, biodegradability of the effluent prior to and after treatment was also evaluated by means of the respirometry technique and the energy consumption of the process was estimated. The analysis of the energy consumption recommends the application of process integration approaches for the treatment of heavily polluted industrial effluents.

A review of imperative technologies for wastewater treatment II: hybrid methods

In the first part of this two article series on the imperative technologies for wastewater treatment, a review of oxidation processes operating at ambient conditions was presented. It has been observed that none of the methods can be used individually in wastewater treatment applications with good economics and high degree of energy efficiency. Moreover, the knowledge required for the large-scale design and application is perhaps lacking. In the present work, an overview of hybrid methods (the majority are a combination of advanced oxidation processes) has been presented. Hybrid methods viz Ultrasound/H 2O 2 or ozone, UV/H 2O 2 or ozone, Ozone/H 2O 2, Sono-photochemical oxidation, Photo–Fenton processes, catalytic advanced oxidation processes, use of advanced oxidation processes in conjunction with biological oxidation, SONIWO (sonochemical degradation followed by wet air oxidation), and CAV-OX have been discussed with specific reference to the principles behind the expected synergism, different reactor configurations used and optimum considerations for the operating and geometric parameters. An overview of different chemicals degraded has been presented. Some of the important works evaluating the application of these processes to real effluents have been described in detail. Some guidelines for the future work required to facilitate efficient large-scale operation have been given. A model effluent treatment scheme based on the various techniques discussed in the present work has been presented.