Critical review of perovskites-based advanced oxidation processes for wastewater treatment: Operational parameters, reaction mechanisms, and prospects

First-principles investigations of Fe-based A3BX ceramics with high stiffness and damage tolerance

In the search for high-stiffness and damage-tolerant materials, Fe-based A3BX carbide and nitride anti-perovskites were studied using first-principles calculations. These perovskites were found to be stable in cubic structures, as substantiated by the formation energy, elastic Born stability criterion, and phonon dispersion spectrum analysis. The GGA functional was applied for geometry optimization, and the lattice constants are found to be 3.730 Å, 3.715 Å, 3.832 Å, and 3.828 Å for Fe3AlC, Fe3AlN, Fe3SnC, and Fe3SnN, respectively. Elastic property analysis reveals that all the materials have large elastic moduli, high sound velocities, and high Debye temperatures. Among them, carbides have superior stiffness and quasi-ductile properties, and they can be further improved by applying additional pressure. Preliminary analysis of electronic properties indicates that they are ferromagnetic and metallic compounds. Their high melting temperatures (>2600 K) confirm their potential in high-temperature applications. The lowest thermal conductivity of Fe3SnN suggests its potential in efficient solid-state refrigeration application. Moreover, Fe3SnC is proposed to be a viable damage-tolerant material with good prospects. Under 10 GPa external pressure, it possesses a ductile structure with a Young's modulus of 402.15 GPa and bulk modulus of 280.25 GPa.

Activation of H2O2-HCO3- by Ca2Co2O5 for pollutant degradation

The bicarbonate-activated hydrogen peroxide (BAP) system is widely studied for organic pollutant degradation in wastewater treatment. Ca2Co2O5, a heterogeneous catalyst containing multivalent cobalt including Co(II) and Co(III), was herein investigated as a BAP activator, and Acid Orange 7 (AO7) was used as a model pollutant. Ca2Co2O5 exhibited good activation performance. The degradation rate and the initial rate constant of the Ca2Co2O5-activated BAP system were 5.4 and 11.2 times as high as the BAP system, respectively. The removal rate of AO7 reached 90.9% in 30 min under optimal conditions (AO7 20 mg/L, Ca2Co2O5 0.2 g/L, H2O2 1 mM, NaHCO3 5 mM, pH 8.5, 25℃). The Ca2Co2O5 catalyst exhibited good stability and recyclability, retaining 85% of AO7 removal rate in the fifth run. Compared to the BAP system, a lower dosage of H2O2 was required and a higher initial concentration of pollutants allowed for effective degradation in the Ca2Co2O5-BAP system. X-ray photoelectron spectroscopy was used to analyze the catalytic mechanism. The analysis showed that the good catalytic performance of Ca2Co2O5 attributes to its high proportion of oxygen vacancies and Co(III) species, and the presence of Ca. The active species O2•-, •OH, and 1O2 are responsible for the degradation, as indicated by the quenching experiments. The degradation mechanism of AO7 was speculated based on UV-Vis spectral analysis and the identification of degradation intermediates. The azo form, naphthalene and benzoic rings in the AO7 structure are destroyed in the decomposition. This research provides a feasible approach to designing effective and reusable BAP activators for pollutant degradation in wastewater treatment.

Electron transfer mediated photo-Fenton-like synergistic catalysis of Fe,Cu-doped MIL-101 coupled with Ag3PO4: Quantitative evaluation and DFT calculations

Widespread use of tetracycline (TC) results in its persistent residue and bioaccumulation in aquatic environments, posing a high toxicity to non-target organisms. In this study, a bimetal-doped composite material Ag3PO4/MIL-101(Fe,Cu) has been designed for the treatment of TC in aqueous solutions. As the molar ratio of Fe/Cu in composite is 1:1, the obtained material AP/MFe1Cu1 is placed in an aqueous environment under visible light irradiation in the presence of 3 mM peroxydisulfate (PDS), which forms a photo-Fenton-like catalytic system that can completely degrade TC (10 mg/L) within 60 min. Further, the degradation rate constant (0.0668 min-1) is 5.66 and 7.34 times higher than that of AP/MFe and AP/MCu, respectively, demonstrating a significant advantage over single metal-doped catalysts. DFT calculations confirm the strong adsorption capacity and activation advantage of PDS on the composite surface. Therefore, the continuous photogenerated electrons (e-) accelerate the activation of PDS and the production of SO4•-, resulting in the stripping of abundant photogenerated h + for TC oxidation. Meanwhile, the internal circulation of FeⅢ/FeⅡ and CuⅡ/CuⅢ in composite also greatly enhances the photo-Fenton-like catalytic stability. According to the competitive dynamic experiments, SO4•- have the greatest contribution to TC degradation (58.93%), followed by 1O2 (23.80%). The degradation intermediates (products) identified by high-performance liquid chromatography-mass spectrometry (HPLC/MS) technique indicate the involvement of various processes in TC degradation, such as dehydroxylation, deamination, N-demethylation, and ring opening. Furthermore, as the reaction proceeds, the toxicity of the intermediates produced during TC degradation gradually decreases, which can ensure the safety of the aquatic ecosystem. Overall, this work reveals the synergy mechanism of PDS catalysis and photocatalysis, as well as provides technical support for removal of TC-contaminated wastewater.

Recent advances in metal halide perovskite based photocatalysts for artificial photosynthesis and organic transformations

Metal halide perovskites (MHP) emerged as highly promising materials for photocatalysis, offering significant advancements in the degradation of soluble and airborne pollutants, as well as the transformation of functional organic compounds. This comprehensive review focuses on recent developments in MHP-based photocatalysts, specifically examining two major categories: lead-based (such as CsPbBr3) and lead-free variants (e.g. Cs2AgBiX6, Cs3Bi2Br9 and others). While the review briefly discusses the contributions of MHPs to hydrogen (H2) production and carbon dioxide (CO2) reduction, the main emphasis is on the design principles that determine the effectiveness of perovskites in facilitating organic reactions and degrading hazardous chemicals through oxidative transformations. Furthermore, the review addresses the key factors that influence the catalytic efficiency of perovskites, including charge recombination, reaction mechanisms involving free radicals, hydroxyl ions, and other ions, as well as phase transformation and solvent compatibility. By offering a comprehensive overview, this review aims to serve as a guide for the design of MHP-based photocatalysis and shed light on the common challenges faced by the scientific community in the domain of organic transformations.

Research progress of persulfate activation technology

Persulfate-based advanced oxidation processes (PS-AOPs) have been widely investigated by academia and industry due to their high efficiency and selectivity for the removal of trace organic pollutants from complex water substrates. PS-AOPs have been extensively studied for the degradation of pesticides, drugs, halogen compounds, dyes, and other pollutants. Utilizing bibliometric statistics, this review presents a comprehensive overview of persulfate-based advanced oxidation technology research over the past decade. The number of published articles about persulfate activation has steadily increased during this time, reflecting extensive international collaboration. Furthermore, this review introduces the most widely employed strategies for persulfate activation reported in the past 10 years, including carbon material activation, photocatalysis, transition metal activation, electrochemical activation, ultrasonic activation, thermal activation, and alkali activation. Next, the potential activation mechanisms and influencing factors, such as persulfate dosage during activation, are discussed. Finally, the application of PS-AOPs in wastewater treatment and in situ groundwater treatment is examined. This review summarizes the previously reported experiences of persulfate-based advanced oxidation technology and presents the current application status of PS-AOPs in organic pollution removal, with the aim of avoiding misunderstandings and providing a solid foundation for future research on the removal of organic pollutants.

Underlying the mechanisms of pathogen inactivation and regrowth in wastewater using peracetic acid-based disinfection processes: A critical review

Peracetic acid (PAA) disinfection is an emerging wastewater disinfection process. Its advantages include excellent pathogen inactivation performance and little generation of toxic and harmful disinfection byproducts. The objective of this review is to comprehensively analyze the experimental data and scientific information related to PAA-based disinfection processes. Kinetic models and modeling frameworks are discussed to provide effective tools to assess pathogen inactivation efficacy. Then, the efficacy of PAA-based disinfection processes for pathogen inactivation is summarized, and the inactivation mechanisms involved in disinfection and the interactions of PAA with conventional disinfection processes are elaborated. Subsequently, the risk of pathogen regrowth after PAA-based disinfection process is clearly discussed. Finally, to address ecological risks related to PAA-based disinfection, its impact on the spread of antibiotic-resistant bacteria and the transfer of antibiotic resistance genes (ARGs) is also assessed. Among advanced PAA-based disinfection processes, ultraviolet/PAA is promising not only because it has practical application value but also because pathogen regrowth can be inhibited and ARGs transfer risk can be significantly reduced via this process. This review presents valuable and comprehensive information to provide an in-depth understanding of PAA as an alternative wastewater disinfection technology.

Enhanced electron transfer for activation of peroxymonosulfate via MoS2 modified iron-based perovskite

The increasing use of fluoroquinolone antibiotics, which are found in various environmental media, is a constant threat to ecological safety and human health. In this paper, SrFeO3@MoS2 heterogeneous catalyst was prepared to activate peroxymonosulfate (PMS) for the degradation of levofloxacin (LVO). The characteristics of SrFeO3@MoS2 samples were studied and the optimum conditions for the removal of LVO by SrFeO3@MoS2/PMS system were investigated. The removal of LVO by the SrFeO3@MoS2-0.3/PMS system could reach 96.06% within 20 min of reaction. The effect of inorganic anions (SO42-, Cl-, NO3- and H2PO4-) commonly found in actual water bodies on catalytic reaction was explored. The reusability investigation revealed that the catalyst could still remove 88.06% of LVO within 20 min after four cycles. Moreover, SO4•-, •OH and 1O2 were identified by Electron Paramagnetic Resonance (EPR) tests and scavenger experiments, where the SO4•- and •OH were dominant reactive species. Combining with the XPS characterisation, the activation mechanism of SrFeO3@MoS2-0.3/PMS was proposed, and the oxygen vacancies and transition metals on the sample surface were active sites of PMS activation. Furthermore, the possible degradation pathways of LVO were well-established based on the detected intermediates.

Application of advanced oxidation processes for the removal of micro/nanoplastics from water: A review

Micro/nanoplastics (MNPs) have been increasingly found in environments, food, and organisms, arousing wide public concerns. MNPs may enter food chains through water, posing a threat to human health. Therefore, efficient and environmentally friendly technologies are needed to remove MNPs from contaminated aqueous environments. Advanced oxidation processes (AOPs) produce a vast amount of active species, such as hydroxyl radicals (·OH), known for their strong oxidation capacity. As a result, an increasing number of researchers have focused on using AOPs to decompose and remove MNPs from water. This review summarizes the progress in researches on the removal of MNPs from water by AOPs, including ultraviolet photolysis, ozone oxidation, photocatalysis, Fenton oxidation, electrocatalysis, persulfate oxidation, and plasma oxidation, etc. The removal efficiencies of these AOPs for MNPs in water and the influencing factors are comprehensively analyzed, meanwhile, the oxidation mechanisms and reaction pathways are also discussed in detail. Most AOPs can achieve the degradation of MNPs, mainly manifest as the decrease of particle size and the increase of mass loss, but the mineralization rate is low, thus requiring further optimization for improved performance. Investigating various AOPs is crucial for achieving the complete decomposition of MNPs in water. AOPs will undoubtedly play a vital role in the future for the removal of MNPs from water.

Peracetic acid disinfection induces antibiotic-resistant E. coli into VBNC state but ineffectively eliminates the transmission potential of ARGs

The occurrence of a viable but nonculturable (VBNC) state in antibiotic-resistant E. coli (AR E. coli) and inefficient degradation of their antibiotic resistance genes (ARGs) may cause potential health risks during disinfection. Peracetic acid (PAA) is an alternative disinfectant for replacing chlorine-based oxidants in wastewater treatment, and the potential of PAA to induce a VBNC state in AR E. coli and to remove the transformation functionality of ARGs were investigated for the first time. Results show that PAA exhibits excellent performance in inactivating AR E. coli (over 7.0-logs) and persistently inhibiting its regeneration. After PAA disinfection, insignificant changes in the ratio of living to dead cells (∼4%) and the level of cell metabolism, indicating that AR E. coli were induced into VBNC states. Unexpectedly, PAA was found to induce AR E. coli into VBNC state by destroying the proteins containing reactive amino acids at thiol, thioether and imidazole groups, rather than the result of membrane damage, oxidative stress, lipid destruction and DNA disruption in the conventional disinfection processes. Moreover, the result of poor reactivity between PAA and plasmid strands and bases confirmed that PAA hardly reduced the abundance of ARGs and damaged the plasmid's integrity. Transformation assays and real environment validation indicated that PAA-treated AR E. coli could release large abundance of naked ARGs with high-efficiency transformation functionality (∼5.4 × 10-4 - ∼8.3 × 10-6) into the environment. This study has significant environmental implications for assessing the transmission of antimicrobial resistance during PAA disinfection.

Simultaneous removal of antibiotics and antibiotic resistance genes in wastewater by a novel nonthermal plasma/peracetic acid combination system: Synergistic performance and mechanism

In this study, a novel and green method combining plasma with peracetic acid (plasma/PAA) was developed to simultaneously remove antibiotics and antibiotic resistance genes (ARGs) in wastewater, which achieves significant synergistic effects in the removal efficiencies and energy yield. At a plasma current of 2.6 A and PAA dosage of 10 mg/L, the removal efficiencies of most detected antibiotics in real wastewater exceeded 90 % in 2 min, with the ARG removal efficiencies ranging from 6.3 % to 75.2 %. The synergistic effects of plasma and PAA could be associated with the motivated production of reactive species (including •OH, •CH₃, ¹O₂, ONOO^-, •O₂^- and NO•), which decomposed antibiotics, killed host bacteria, and inhibited ARG conjugative transfer. In addition, plasma/PAA also changed the contributions and abundances of ARG host bacteria and downregulated the corresponding genes of two-component regulatory systems, thus reducing ARG propagation. Moreover, the weak correlations between the removal of antibiotics and ARGs highlights the commendable performance of plasma/PAA in the simultaneous removal of antibiotics and ARGs. Therefore, this study affords an innovative and effective avenue to remove antibiotics and ARGs, which relies on the synergistic mechanisms of plasma and PAA and the simultaneous removal mechanisms of antibiotics and ARGs in wastewater.

Immobilized microalgal system: An achievable idea for upgrading current microalgal wastewater treatment

Efficient wastewater treatment accompanied by sustainable "nutrients/pollutants waste-wastewater-resources/energy nexus" management is acting as a prominent and urgent global issue since severe pollution has occurred increasingly. Diverting wastes from wastewater into the value-added microalgal-biomass stream is a promising goal using biological wastewater treatment technologies. This review proposed an idea of upgrading the current microalgal wastewater treatment by using immobilized microalgal system. Firstly, a systematic analysis of microalgal immobilization technology is displayed through an in-depth discussion on why using immobilized microalgae for wastewater treatment. Subsequently, the main technical approaches employed for microalgal immobilization and pollutant removal mechanisms by immobilized microalgae are summarized. Furthermore, from high-tech technologies to promote large-scale production and application potentials in diverse wastewater and bioreactors to downstream applications lead upgradation closer, the feasibility of upgrading existing microalgal wastewater treatment into immobilized microalgal systems is thoroughly discussed. Eventually, several research directions are proposed toward the future immobilized microalgal system for microalgal wastewater treatment upgrading. Together, it appears that using immobilization for further upgrading the microalgae-based wastewater treatment can be recognized as an achievable alternative to make microalgal wastewater treatment more realistic. The information and perspectives provided in this review also offer a feasible reference for upgrading conventional microalgae-based wastewater treatment.

Thiosulfate enhanced Cu(II)-catalyzed Fenton-like reaction at neutral condition: Critical role of sulfidation in copper cycle and Cu(III) production

Thiosulfate (S₂O₃^2-) has been proven to be an effective promoter of Fenton-like reactions by accelerating the metal ions cycle. However, up to now, little is known about the role of sulfur transformation and intermediate sulfur in the regulation of metal chemical cycle and reactive species production. Herein, free Cu(II) was selected as catalyst for the activation of H₂O₂. The introduction of S₂O₃^2- significantly enhanced the degradation of benzoic acid, and the degradation rate (k_obs) was 5.8 times that of Cu(II)/H₂O₂ system. The kinetic model revealed the transformation of sulfur species and demonstrated that sulfides (i.e., HS^-/S^2-, S₂O₃^2-) and S⁰ were the dominant electron donor for the reduction of Cu(II) into Cu(I). Consequently, the reduction and complexation roles of S₂O₃^2- significantly resolve the rate-limiting step and broaden the pH range of in Fenton-like reactions. Evidence for the critical role of high-valent copper (Cu(III)) and HO^• on BA degradation was obtained by scavengers experiments, electron paramagnetic resonance and fluorescent probes. Meanwhile, the Cu(II)/H₂O₂/S₂O₃^2- system also exhibited satisfactory anti-interference ability of the various matrix. Overall, this study offers mechanistic insight into sulfidation in Cu chemical cycle and Cu(III) generation, and highlights the potential of S₂O₃^2- for Fenton-like reactions to control pollutants.

Co-Mn spinel oxides trigger peracetic acid activation for ultrafast degradation of sulfonamide antibiotics: Unveiling critical role of Mn species in boosting Co activity

Activation of peracetic acid (PAA) to generate powerful oxidizing species has become a promising advanced oxidation processes (AOPs) in wastewater treatment, yet the development of low-cost and high-performance activators is still a primary challenge. Herein, a range of Co-Mn spinel oxides (Co_3-xMn_xO₄) with varying levels of Co and Mn were successfully elaborated, in which Co_1.1Mn_1.9O₄ exhibited remarkable performance in PAA activation, outperforming most reported heterogeneous catalysts. Extensive quenching experiments and electron spin resonance (ESR) analysis indicated that acetylperoxyl radical (CH₃C(O)OO^●) was the predominated oxidizing species responsible for sulfamethoxazole (SMX) degradation. Density functional theory (DFT) calculations revealed that doping with Mn not only promoted the electron transfer and accelerated reduction of Co(III) to Co(II), but also lowered the energy barrier for PAA activation. Moreover, the prominent chemisorption and activation of PAA with Co_1.1Mn_1.9O₄ was also benefitted from the significant role of Mn in optimizing the distribution of bonding and antibonding states on Co 3d orbitals. Unexpectedly, high levels of Cl^-greatly facilitated SMX degradation due to the mass production of HOCl from the chain reactions of various radicals with Cl^-. This work provides new insights into bimetallic activation of PAA, and the knowledge obtained will further advance the application of PAA-based AOPs.

Physiological and morphological responses of Chlorella pyrenoidosa to different exposure methods of graphene oxide quantum dots

Graphene oxide quantum dots (GOQDs) can convert the ultraviolet (200- 380 nm) into available wavelength (400- 700 nm) for microalgae cultivation. However, it has not been applied in large-scale microalgae culture due to its high cost and difficulties in recovery. This study proposed a new strategy for the sustainable use of GOQDs, namely, GOQDs solution was added to the outer sandwich of the reactor. Herein, the effects of direct and indirect exposure of different GOQDs concentrations (0, 100, and 1000 mg/L) on the microalgae culture were compared. When microalgae were directly exposed to the GOQDs, 100 mg/L of GOQDs increased the biomass production of microalgae by 24.0 %, while 1000 mg/L of GOQDs decreased biomass production by 31 %. High concentration of GOQDs (direct exposure) could cause extra oxidative stress in the microalgae cells and result in a significant reduction of pigment content. When microalgae were indirectly exposed to the GOQDs, the increased concentration of GOQDs enhanced the growth of microalgae. Compared to the blank group, 1000 mg/L of GOQDs increased the microalgae biomass production and bioenergy by 14.1 % and 40.17 %, respectively. The indirect exposure of GOQDs can effectively avoid photo-oxidation and organelle damage to the microalgae cells. Overall, the indirect exposure of GOQDs is a sustainable way for effectively promoting microalgae growth and reducing the application cost.

Simultaneous removal of carbamazepine and Cd(II) in groundwater by integration of peroxydisulfate oxidation and sulfidogenic process: The bridging role of SO42

Heat-activated PDS oxidation (HAPO) has been widely used for in-situ chemical oxidation (ISCO) of micropollutants in groundwater, whereas the aesthetic demerit of additional SO₄^2- production is largely overlooked. In this study, the sulfidogenic process is used to offset the aesthetic demerit, and the production of SO₄^2- is then employed to recycle heavy metals. The innovative integration technology with PDS oxidation and sulfidogenic process via the bridging role of SO₄^2- was reported to remove micropollutants and heavy metals in groundwater simultaneously. HAPO could completely degrade CBZ, producing 400 mg/L SO₄^2- with the addition of 0.50 g/L PDS. Sulfate-reducing bacteria (SRB) utilize SO₄^2- generated from HAPO as the electron acceptor in the sulfidogenic process, removing and recycling Cd(II) via the precipitation of CdS. The SRB tolerance experiment revealed the viability of PDS oxidation coupled with the sulfidogenic process via the bridging role of SO₄^2-. Overall, the integration technology is a green and promising technology for simultaneous micropollutants removal and heavy metals recycling in groundwater.

Romo AI, Pudar S, Putnam ST, Bustos E, Rodríguez-López J. Real-Time Detection of Hydroxyl Radical Generated at Operating Electrodes via Redox-Active Adduct Formation Using Scanning Electrochemical Microscopy

The hydroxyl radical (•OH) is one of the most attractive reactive oxygen species due to its high oxidation power and its clean (photo)(electro)generation from water, leaving no residues and creating new prospects for efficient wastewater treatment and electrosynthesis. Unfortunately, in situ detection of •OH is challenging due to its short lifetime (few ns). Using lifetime-extending spin traps, such as 5,5-dimethyl-1-pyrroline N-oxide (DMPO) to generate the [DMPO-OH]• adduct in combination with electron spin resonance (ESR), allows unambiguous determination of its presence in solution. However, this method is cumbersome and lacks the necessary sensitivity and versatility to explore and quantify •OH generation dynamics at electrode surfaces in real time. Here, we identify that [DMPO-OH]• is redox-active with E0 = 0.85 V vs Ag|AgCl and can be conveniently detected on Au and C ultramicroelectrodes. Using scanning electrochemical microscopy (SECM), a four-electrode technique capable of collecting the freshly generated [DMPO-OH]• from near the electrode surface, we detected its generation in real time from operating electrodes. We also generated images of [DMPO-OH]• production and estimated and compared its generation efficiency at various electrodes (boron-doped diamond, tin oxide, titanium foil, glassy carbon, platinum, and lead oxide). Density functional calculations, ESR measurements, and bulk calibration using the Fenton reaction helped us unambiguously identify [DMPO-OH]• as the source of redox activity. We hope these findings will encourage the rapid, inexpensive, and quantitative detection of •OH for conducting informed explorations of its role in mediated oxidation processes at electrode surfaces for energy, environmental, and synthetic applications.

Heterogeneous Activation of Peroxymonosulfate by a Spinel CoAl2O4 Catalyst for the Degradation of Organic Pollutants

Bimetallic catalysts have significantly contributed to the chemical community, especially in environmental science. In this work, a CoAl2O4 spinel bimetal oxide was synthesized by a facile co-precipitation method and used for the degradation of organic pollutants through peroxymonosulfate (PMS) activation. Compared with Co3O4, the as-prepared CoAl2O4 possesses a higher specific surface area and a larger pore volume, which contributes to its becoming increasingly conducive to the degradation of organic pollutants. Under optimal conditions (calcination temperature: 500 °C, catalyst: 0.1 g/L, and PMS: 0.1 g/L), the as-prepared CoAl2O4 catalyst could degrade over 99% of rhodamine B (RhB) at a degradation rate of 0.048 min−1, which is 2.18 times faster than Co3O4 (0.022 min−1). The presence of Cl− could enhance RhB degradation in the CoAl2O4/PMS system, while HCO3− and CO32− inhibit RhB degradation. Furthermore, the considerable reusability and universality of CoAl2O4 were testified. Through quenching tests, 1O2 and SO4•− were identified as the primary reactive species in RhB degradation. The toxicity evaluation verified that the degraded solution exhibited lower biological toxicity than the initial RhB solution. This study provides new prospects in the design of cost-effective and stable cobalt-based catalysts and promotes the application of PMS-based advanced oxidation processes for refractory wastewater treatment.