Degradation Of Micropollutants Research Articles

Heat-activated persulfate for the degradation of micropollutants in water: A comprehensive review and future perspectives.

This work is a critical review of the most important studies that have dealt with heat-activated persulfate to degrade persistent micropollutants in the last six years. The effect of the different operating parameters is discussed, wherein in all cases, the efficiency was favored at higher temperatures and oxidant concentrations. Particular emphasis was given to the effect of the aqueous matrix. Since heat activation is a homogeneous process based on the production of free radicals, in most of the studies presented, the removal of pollutants decreases as the complexity of the aqueous matrix increases except in cases where secondary oxidative species are produced that are selective with specific pollutants. It has also been observed that the change in toxicity usually follows the removal of the parent compound despite the formation of several by-products. Nowadays, combining different processes for the simultaneous activation of persulfate seems to be gaining ground. A hybrid process is an interesting strategy to reduce costs and increase efficiency, especially in real wastewater. In this light, the most interesting studies of hybrid systems for the destruction of micropollutants in recent years based on thermally activated persulfate are also summarized. Finally, some steps are proposed for future research towards the industrial application, including the study of chemical mixtures, the integrated toxicity assessment, the examination of simultaneous disinfection and decomposition of pollutants into real wastewater, the estimation of the required costs, and energy the combination of processes and their coupling with renewable sources, and the design of pilot plants and the scale-up of the hybrid processes.

New insights into the degradation of micro-pollutants in the hydroxylamine enhanced Fe(II)/peracetic acid process: Contribution of reactive species and effects of pH

The hydroxylamine-enhanced Fe(II)/peracetic acid (PAA) process is a promising advanced oxidation process (AOP) with the generation of reactive species (RS) including RO•, •OH and Fe(IV). Nevertheless, it is still challenging to identify which RS is the major intermediate oxidant, and the reasons why the optimal condition is pH 4.5 rather than 3.0 are also unclear. Herein, the generation of RS and their contribution to the degradation of three micro-pollutants were explored. The quenching experiments and pseudo first-order kinetic model demonstrated that RO• rather than the other two RS were predominant. Then the overall generation and evolution pathways of RS were depicted. The elevation of pH (3.0–4.5) would accelerate the Fe(II)/Fe(III) redox cycle through the enhanced reduction of Fe(III) by hydroxylamine and induce the conversion of Fe(IV) to RO•, which benefited naproxen degradation. While the adverse Fe(III) precipitation would dominate the reduced degradation performance with the solution pH higher than 4.5. The elevation of PAA and Fe(II) dosages sped up the PAA activation, while excess hydroxylamine could consume the formed RS and exhibited an inhibitory effect. This study helps further understand the role of HA and differentiate the contribution of RS in the emerging PAA-based AOPs.

Effect of Iron Complex Source on MWWTP Effluent Treatment by Solar Photo-Fenton: Micropollutant Degradation, Toxicity Removal and Operating Costs.

Benzophenone-3, fipronil and propylparaben are micropollutants that are potential threats to ecosystems and have been detected in aquatic environments. However, studies involving the investigation of new technologies aiming at their elimination from these matrices, such as advanced oxidation processes, remain scarce. In this study, different iron complexes (FeCit, FeEDTA, FeEDDS and FeNTA) were evaluated for the degradation of a mixture of these micropollutants (100 µg L−1 each) spiked in municipal wastewater treatment plant (MWWTP) effluent at pH 6.9 by solar photo-Fenton. Operational parameters (iron and H2O2 concentration and Fe/L molar ratio) were optimized for each complex. Degradation efficiencies improved significantly by increasing the concentration of iron complexes (1:1 Fe/L) from 12.5 to 100 µmol L−1 for FeEDDS, FeEDTA and FeNTA. The maximum degradation reached with FeCit for all iron concentrations was limited to 30%. Different Fe/L molar ratios were required to maximize the degradation efficiency for each ligand: 1:1 for FeNTA and FeEDTA, 1:3 for FeEDDS and 1:5 for FeCit. Considering the best Fe/L molar ratios, higher degradation rates were reached using 5.9 mmol L−1 H2O2 for FeNTA and FeEDTA compared to 1.5 and 2.9 mmol L−1 H2O2 for FeEDDS and FeCit, respectively. Acute toxicity to Canton S. strain D. melanogaster flies reduced significantly after treatment for all iron complexes, indicating the formation of low-toxicity by-products. FeNTA was considered the best iron complex source in terms of the kinetic constant (0.10 > 0.063 > 0.051 > 0.036 min−1 for FeCit, FeNTA, FeEDTA and FeEDDS, respectively), organic carbon input and cost-benefit (USD 327 m−3 > USD 20 m−3 > USD 16 m−3 > USD 13 m−3 for FeEDDS, FeCit, FeEDTA and FeNTA, respectively) when compared to the other tested complexes.

Enhanced photocatalytic efficiency via improved contact in a solar-driven membrane reactor for steroid hormone removal

The application of solar-driven photocatalytic membranes (PM) for steroid hormone elimination from surface water is encouraging. However, both the limited availability and utilization of oxidizing species (singlet oxygen) inside the PM and the limited diffusion of reactants may constrain the destruction of organic pollutants. To facilitate the contact between the liquid phase and PM surface, poly(vinylidene-fluoride) membranes with small pore size are used to confine and evenly distribute organic photocatalyst (porphyrin) molecules. The porphyrin-coated membranes with nanopores (20 nm, NM20) provide a greater surface area and four times faster degradation of 17β-estradiol than PMs based on microfiltration membranes (pore size in range 100 – 650 nm). Stacking multiple NM20 membranes on top of each other extends contact time and results in a concentration of 17β-estradiol in the permeate of 2 ng L–1, but the gain in 17β-estradiol removal is limited by light propagation. Alternatively, adjusting the flux (below 150 L m–2 h−1) of the membrane with pore size of 200 nm is effective in reducing the concentration of 17β-estradiol in the permeate from 100 ng L–1 to 1 ng L–1. These results ensure the compliance with the European Commission guidance value for 17β-estradiol. The degradation of more chemically stable testosterone (compared to 17β-estradiol and estrone) using NM20 membranes is improved relative to PM with larger pores (200 nm). This study confirms that improved contact, achieved by carefully choosing the membrane support, accelerates the photocatalytic degradation of micropollutants.

H2O2 activation by two-dimensional metal-organic frameworks with different metal nodes for micropollutants degradation: Metal dependence of boosting reactive oxygen species generation

The existence of organic micropollutants (OPMs) in water poses a considerable threat to the environment. A centralized approach towards pollutants abatement has dominated over the recent decades wherein heterogeneous Fenton-like based advanced oxidation processes can be a promising technology. The application of engineered nanomaterials offers more opportunities to enhance their catalyst properties. This study synthesizes a series of ultrathin two-dimensional (2D) Metal-organic frameworks (MOFs) nanosheets with tunable metal clusters. The formation of reactive oxygen species (•OH and 1O2) can be significantly boosted via transferring the adsorbed H2O2 onto the solid-liquid interface by systematically tuning the metal species. The Co-MOF nanosheets exhibited an ultrafast degradation kinetic for BPA with a rate of 2.23 min−1 (4.98 times higher than that of the bulk MOF) and TOF (turnover frequency) value of 9.99 min−1, which are observably greater than that of the existing materials reported to date. Density functional theory simulation and experimental results unravel the mechanism for ROS formation, which is strongly metal-depend. We further loaded the powder onto a flow-through poly (vinylidene fluoride) (PVDF) microfiltration membrane and observed that the representative OPMs could be rapidly degraded, indicating promising properties for practical application.

Degradation of micropollutants in flow-through UV/chlorine reactors: Kinetics, mechanism, energy requirement and toxicity evaluation

The degradation of three micropollutants (i.e., atrazine (ATZ), sulfamethoxazole (SMX) and metoprolol (MET)) was comprehensively investigated in flow-through UV/chlorine reactors. Results showed that the micropollutants degradation fitted well with pseudo-first-order kinetics (R2 > 0.92) with the order of rate constants following SMX > MET > ATZ. The developed steady-state approximation (SSA) model was roughly applicable in flow-through UV/chlorine reactors with the predictions deviated within 44%. UV photolysis here stood as the major degradation pathway for ATZ while the contribution of non-radical processes (UV photolysis and chlorination) to SMX degradation increased as the reactor internal diameter enlarged. The degradation rates were reduced to varying extents with complex water matrices (chloride, bicarbonate and dissolved organic matter (DOM)) where the inhibition from the DOM was most prominent (up to 73.6%). Although reactors with a larger internal diameter resulted in reduced degradation rate constants, the energy requirements were also lowered. The EEO values of micropollutants degradation by UV/chlorine fell mostly within 1.0 kWh m−3 order−1 in deionized water and under different water matrices. The acute toxicity was observed to be higher after UV/chlorine treatment in tap water, but still stayed low in general. This study revealed the different kinetics and mechanisms of micropollutants degradation in flow-through reactors and demonstrated the potential of the UV/chlorine process in terms of low energy consumption and acute toxicity.

Quantification of the diverse inhibitory effects of dissolved organic matter on transformation of micropollutants in UV/persulfate treatment

Dissolved organic matter (DOM), ubiquitous in natural waters, is known to inhibit the degradation of micropollutants in the advanced oxidation processes such as the UV/peroxydisulfate process. However, the quantitative understanding of the inhibitory pathways is missing. In this study, guanosine, aniline and catechol belonging to amines, purines and phenols were first investigated due to their resistance to UV irradiation at 254 nm and similar reactivity with SO4•− and HO•, respectively. The presence of 0.5 mgC L−1 Suwannee River NOM (SRNOM) inhibited their degradation rates by 72.9%, 54.5%, and 32.4%, respectively, despite their similar degradation rates in the absence of SRNOM. The results highlight the importance of reverse reduction of oxidation intermediates to the parent compound by antioxidant moieties in SRNOM besides the inner filtering and radical scavenging effects. The three inhibitory pathways were quantified for 34 common micropollutants. In the presence of 0.5 mgC L−1 SRNOM, inner filtering effect was found to contribute less than 2.8% of the inhibitory percentages (IP). Radical scavenging effects contribute between 10.7% and 38.9% and compounds having lower reactivity with SO4•− (< 4.0 × 109 M−1 s−1) tended to be inhibited more strongly. The IP of reverse reduction effects of SRNOM varied significantly from none up to 70.8%. It was linearly related with a micropollutant's reduction potential. Purines and amines generally exhibited more pronounced reverse reduction inhibition than phenols. The results of this study provide guidance on improving the elimination efficiency of micropollutants.

The binding effect and photooxidation on oxytetracycline with algal extracellular polymeric substances and natural organic matter

Surface water contains a large amount of dissolved organic matter (DOM). Interactions between DOM and micropollutants have a significant impact on micropollutant degradation. In this study, algal extracellular polymeric substances (EPS) and natural organic matter (NOM) were selected as two DOM sources and oxytetracycline (OTC) as a representative micropollutant. EPS was mainly composed of tryptophan and protein-like organics, while NOM was mainly composed of fulvic acid-like, humic acid-like, and hydrophobic acid components. In addition, OTC degradation significantly decreased when bound with EPS and the C=O and C–H bonds of CH2 or CH3 groups may be involved in binding EPS and OTC, respectively, while –COOH may be involved in the binding of NOM and OTC. Furthermore, triplet intermediates were found to play a major role in OTC photodegradation in both EPS and NOM, with the contribution calculated as 49.96% and 44.61%, respectively. Steady-state concentrations of 3EPS* in EPS and 3NOM* in NOM were 3.59 × 10−14 mol L−1 and 5.54 × 10−15 mol L−1, respectively. These results provide new insights into the degradation of antibiotic-containing wastewater in the natural environment or engineering applications.

Reaction of Chlorine Dioxide with Saturated Nitrogen-Containing Heterocycles and Comparison with the Micropollutant Behavior in a Real Water Matrix.

Chlorine dioxide (ClO2) is a very selective oxidant that reacts with electron-rich moieties such as activated amines and thus can degrade specific N-containing micropollutants. N-containing heterocycles (NCHs) are among the most frequent moieties of pharmaceuticals. In this study, the reactions of ClO2 with ritalinic acid and cetirizine, two abundant micropollutants, and model compounds representing their NCH moiety were investigated. The pH-dependent apparent reaction rates of all NCHs with ClO2 were measured and modeled. This model showed that neutral amines are the most important species having reaction rates between 800 and 3200 M-1 s-1, while cationic amines are not reactive. Ritalinic acid, cetirizine, and their representative model compounds showed a high stoichiometric ratio of ≈5 moles ClO2 consumption per degraded ritalinic acid and ≈4 moles ClO2 consumption per degraded cetirizine, respectively. Investigation of chlorine-containing byproducts of ClO2 showed that all investigated NCHs mostly react by electron transfer and form above 80% chlorite. The reactions of the model compounds were well comparable with cetirizine and ritalinic acid, indicating that the model compounds indeed represented the reaction centers of cetirizine and ritalinic acid. Using the calculated apparent reaction rate constants, micropollutant degradation during ClO2 treatment of surface water was predicted for ritalinic acid and cetirizine with -8 to -15% and 13 to -22% error, respectively. The results indicate that in ClO2-based treatment, piperidine-containing micropollutants such as ritalinic acid can be considered not degradable, while piperazine-containing compounds such as cetirizine can be moderately degraded. This shows that NCH model compounds could be used to predict micropollutant degradation.

Reduced Graphene Oxide Triggers Peracetic Acid Activation for Robust Removal of Micropollutants: The Role of Electron Transfer.

Peracetic acid (PAA) serves as a potent and low-toxic oxidant for contaminant removal. Radical-mediated catalytic PAA oxidation processes are typically non-selective, rendering weakened oxidation efficacy under complex water matrices. Herein, we explored the usage of reduced graphene oxide (rGO) for PAA activation via a non-radical pathway. Outperforming the most catalytic PAA oxidation systems, the rGO-PAA system exhibits near-complete removal of typical micropollutants (MPs) within a short time (<2 min). Non-radical direct electron transfer (DET) from MPs to PAA plays a decisive role in the MP degradation, where accelerated DET is achieved by a higher potential of the rGO-PAA reactive surface complexes. Benefitting from DET, the rGO-PAA system shows robust removal of multiple MPs under complex water matrices and with low toxicity. Notably, in the DET regime, the electrostatic attraction of rGO to both PAA and target MP is a critical prerequisite for achieving efficient oxidation, depending on the conditions of solution pH and MP pKa. A heatmap model building on such an electrostatic interaction is further established as guidance for regulating the performance of the DET-mediated PAA oxidation systems. Overall, our work unveils the imperative role of DET for rGO-activated PAA oxidation, expanding the knowledge of PAA-based water treatment strategies.

Integrated adsorptive and photocatalytic degradation of pharmaceutical micropollutant, ciprofloxacin employing biochar-ZnO composite photocatalysts

The expensive carbonaceous substrates including graphene, reduced graphene oxide, carbon nanotubes have been coupled with ZnO to improve the properties and photocatalytic performance of carbon based ZnO photocatalysts. To replace these expensive materials, biochar offers as a low-cost alternative to prepare biochar-based photocatalysts. In this study, Calotropis gigantea leaves derived biochar-ZnO (BC-ZnO) composites were synthesized to overcome the ZnO related problems (charge recombination, wider band gap, and poor visible light absorption). Different BC-ZnO (BCZ-1–3) composites were characterized to evaluate their intrinsic properties and composites were employed to degrade ciprofloxacin (CIP). BCZ-3 composite exhibited slower recombination of electron-hole pairs, lower band gap (2.97 eV), and better light absorption in visible region than ZnO. The enhanced adsorptive-photocatalytic degradation efficiency was attained up to 98.5% using BCZ-3 than BC (46.2%) and ZnO (41.4%). The O2∙- and OH• radicals within BCZ-3 are dominant reactive species indulged in CIP photocatalytic degradation. BCZ-3 photocatalyst exhibits 80% degradation of CIP after four regeneration cycles. The maximum adsorption capacity was achieved 54.18 mg g−1 for BCZ-3 than BC (46.20 mg g−1) and ZnO (15.55 mg g−1). The results show that BCZ-X composites can be used as stable, efficient, economical, and sustainable composite for the recovery of pharmaceutical wastewater.

Oxidation of micropollutants by visible light active graphitic carbon nitride and ferrate(VI): Delineating the role of surface delocalized electrons

The treatment of recalcitrant micropollutants in water remains challenging. Ferrate(VI) (FeVIO42−, Fe(VI)) has emerged as a green oxidant to oxidize organic molecules, however, its reactivity with recalcitrant micropollutants are sluggish. Our results demonstrate enhanced oxidation of carbamazepine (CBZ) by three types of visible light-responsive graphitic carbon nitride (g-C3N4) photocatalyst in absence and presence of ferrate(VI) (FeVIO42−, Fe(VI)) under mild alkaline conditions. The g-C3N4 photocatalysts were prepared by thermal process using urea, thiourea, and melamine and were named as CN-U, CN-T, and CN-M, respectively. The degradation efficiency of CBZ, in both visible light-g-C3N4 and visible light-g–C3N4–FeVIO42- systems followed the order of CN-U > CN-T > CN-M. The mechanisms for this trend was elucidated by measuring physiochemical properties of the microstructures with various surface and analytical techniques. Results suggest the dominating role of specific surface area and surface delocalized electrons of microstructures in degrading CBZ. Crystallinity, morphology, and surface functional groups may not directly associate with CBZ degradation. The CN-U has higher specific surface area and surface delocalized electrons than CN-T and CN-M and therefore the highest degradation efficiency of CBZ. The surface electrons likely generated O2●- and 1O2 in the visible light-g-C3N4 system. The additional oxidants, FeV and FeIV in the visible light-g–C3N4– FeVIO42− system led to higher degradation efficiency than the visible light-g-C3N4 system. Results suggest that the surfaces of g-C3N4 may be prepared preferentially with high levels of delocalized electrons at the surface of microstructures to enhance degradation of micropollutants.

Peracetic Acid Enhances Micropollutant Degradation by Ferrate(VI) through Promotion of Electron Transfer Efficiency.

Ferrate(VI) and peracetic acid (PAA) are two oxidants of growing importance in water treatment. Recently, our group found that simultaneous application of ferrate(VI) and PAA led to much faster degradation of micropollutants compared to that by a single oxidant, and this paper systematically evaluated the underlying mechanisms. First, we used benzoic acid and methyl phenyl sulfoxide as probe compounds and concluded that Fe(IV)/Fe(V) was the main reactive species, while organic radicals [CH3C(O)O•/CH3C(O)OO•] had negligible contribution. Second, we removed the coexistent hydrogen peroxide (H2O2) in PAA stock solution with free chlorine and, to our surprise, found the second-order reaction rate constant between ferrate(VI) and PAA to be only about 1.44 ± 0.12 M-1s-1 while that of H2O2 was as high as (2.01 ± 0.12) × 101 M-1s-1 at pH 9.0. Finally, further experiments on ferrate(VI)-bisulfite and ferrate(VI)-2,2'-azino-bis(3-ethylbenzothiazoline-6-sulfonic)acid systems confirmed that PAA was not an activator for ferrate(VI). Rather, PAA could enhance the oxidation capacity of Fe(IV)/Fe(V), making their oxidation outcompete self-decay. This study, for the first time, reveals the ability of PAA to promote electron transfer efficiency between high-valent metals and organic contaminants and confirms the benefits of co-application of ferrate(VI) and PAA for alkaline wastewater treatment.

Metal-free catalysis for organic micropollutant degradation in waste activated sludge via poly(3-hydroxybutyrate) biopolymers using Cupriavidus sp. L7L coupled with peroxymonosulfate

This study employed a novel and environment-friendly biopolymer/oxidant catalytic system, viz., poly(3-hydroxybutyrate)/peroxymonosulfate (PHB/PMS), for pretreating wastewater sludge for the first time. Under optimal conditions, i.e., 3.1 × 10−4 M of PMS and 3.3 g/L of PHB at pH = 6.0, the PAHs in the sludge matrix was decreased by 79 % in 12 h. Increase in salinity (75 % synthetic seawater) achieved 83 % of PAHs degradation. Functional groups (CO) of the biopolymer matrix were active centers for biopolymer-mediated electron transfer that produced reactive oxygen species (SO4−, HO, and 1O2) for adsorption and catalytic oxidation of PAHs in the sludge. Functional metagenomic analysis revealed the main genus, Conexibacter (phylum, Actinobacteria) exhibited PAH-degrading function with high efficiency in the biodegradation of PAHs from sludge pretreated with PHB/PMS. Coupling chemical oxidation and biostimulation using bacterial polymer-based biomaterials is effective and beneficial for pretreating wastewater sludge toward circular bioeconomy.

Peracetic acid activation by mechanochemically sulfidated zero valent iron for micropollutants degradation: Enhancement mechanism and strategy for extending applicability

In this study, mechanically sulfidated microscale zero valent iron (S-ZVI) was found to effectively activate the peracetic acid (PAA) with a result of almost complete degradation of six micropollutants within 10 min under neutral conditions, and > 95% sulfamethoxazole (SMX) removal after six cycles. Reactive oxidized species (ROS) including HO•, carbon-centered radicals, and Fe(IV) were generated in the S-ZVI/PAA system, while HO• was the main contributor towards micropollutants degradation. This study clearly revealed that enhancement of the electron donating ability of ZVI by the formed conductive iron sulfides was crucial for promoted Fe(II) generation and subsequent PAA activation over several cycles, rather than the ability of sulfides to reduce Fe(III) for Fe(II) regeneration as reported previously. Interestingly, it's discovered that co-existence of Fe(III) would dramatically improve the contaminants removal efficiency of the S-ZVI/PAA system; transform the surfaced Fe(II) dominated ROS generation process to aqueous Fe(II) one; enhance the tolerance of the proposed system to water matrix. The promoting effect of predosed Fe(III) on PAA activation by S-ZVI should be mainly associated with: the greater ability of Fe(III) than H2O to accept electron from Fe0 for obtaining more active sites; slower Fe0 consumption and solid sulfur species release for elevated electron utilization efficiency and PAA activation. Considering the convenient and cost-effective access of Fe(III), the decrease of acute toxicity of treated SMX, excellent stability and good removal of various micropollutants fully demonstrate the superiority of S-ZVI/PAA system for practical application.

Superfast degradation of micropollutants in water by reactive species generated from the reaction between chlorine dioxide and sulfite

Chlorine dioxide (ClO2) is used as an oxidant or disinfectant in (waste)water treatment, whereas sulfite is a prevalent reducing agent to quench the excess ClO2. This study demonstrated that seven micropollutants with structural diversity could be rapidly degraded in the reaction between ClO2 and sulfite under environmentally relevant conditions in synthetic and real drinking water. For example, carbamazepine, which is recalcitrant to standalone ClO2 or sulfite, was degraded by 55%–80% in 10 s in the ClO2/sulfite process at 30-µM ClO2 and 30-µM sulfite concentrations within a pH range of 6.0–11.0. Results from experiments and a kinetic model supported that chlorine monoxide (ClO·) and sulfate radicals (SO4·–) were generated in the ClO2/sulfite process, while hydroxyl radical generation was insignificant. Apart from radicals, dichlorine trioxide (Cl2O3) was generated and largely contributed to micropollutant degradation, supported by experimental results using stopped-flow spectrometry and quantum chemical calculations. The impacts of pH, sulfite dosage, and water matrix components (chloride, bicarbonate, and natural organic matter) on micropollutant abatement in the ClO2/sulfite process were evaluated and discussed. When treating the real potable water, the concentrations of organic (five regulated disinfection byproducts) and inorganic byproducts (chlorite and chlorate) formed in the ClO2/sulfite process were all below the drinking water standards. This study disclosed fundamental knowledge advancements relevant to the reaction mechanisms between ClO2 and sulfite, and highlighed a novel process to abate micropollutants in water and wastewater.

Preferential Destruction of Micropollutants in Water through a Self-Purification Process with Dissolved Organic Carbon Polar Complexation.

Removing micropollutants in real water is a scientific challenge due to primary dissolved organic carbon (DOC) and high energy consumption of current technologies. Herein, we develop a self-purification process for the preferential destruction of various micropollutants in municipal wastewater, raw drinking water, and ultrapure water with humic acid (HA) driven by the surface microelectronic field of Fe0-FeyCz/Fex-GZIF-8-rGO without any additional input. It was verified that a strongly polar complex consisting of an electron-rich HA/DOC area and an electron-poor micropollutant area was formed between HA/DOC and micropollutants, promoting more electrons of micropollutants in the adsorbed complex to delocalizing to electron-rich Fe species area and be trapped by O2, which resulted in their surface cleavage and hydrolyzation preferentially. The higher micropollutant degradation efficiency observed in real wastewaters was due to the greater complex polarity of DOC. Moreover, the electron transfer process ensured the stability of the surface microelectronic field and continuous water purification. Our findings provide a new insight into low-energy combined-micropollution water treatment.

Sonophotocatalysis—Limits and Possibilities for Synergistic Effects

Advanced oxidation processes are promising techniques for water remediation and degradation of micropollutants in aqueous systems. Since single processes such as sonolysis and photocatalysis exhibit limitations, combined AOP systems can enhance degradation efficiency. The present work addresses the synergistic intensification potential of an ultrasound-assisted photocatalysis (sonophotocatalysis) for bisphenol A degradation with a low-frequency sonotrode (f = 20 kHz) in a batch-system. The effects of energy input and suspended photocatalyst dosage (TiO2-nanoparticle, m = 0–0.5 g/L) were investigated. To understand the synergistic effects, the sonication characteristics were investigated by bubble-field analysis, hydrophone measurements, and chemiluminescence of luminol to identify cavitation areas due to the generation of hydroxyl radicals. Comparing the sonophotocatalysis with sonolysis and photocatalysis (incl. mechanical stirring), synergies up to 295% and degradation rates of up to 1.35 min−1 were achieved. Besides the proof of synergistic intensification, the investigation of energy efficiency for a degradation degree of 80% shows that a process optimization can be realized. Thus, it could be demonstrated that there is an effective limit of energy input depending on the TiO2 dosage.

Boosting the photocatalytic performance of Bi2Fe4O9 through formation of Z-scheme heterostructure with In2S3: Applications towards water decontamination

Design of biocompatible nano-heterostructure photocatalyst with broad UV–visible spectrum response and strong redox ability is a promising approach with potential application in micropollutant degradation and pathogen deactivation from aqueous sources. Herein, we have reported the facile fabrication of In2S3/Bi2Fe4O9 (ISxBFO) binary heterostructure by hydrothermally depositing In2S3 nanoparticles (20–40 nm) over Bi2Fe4O9 nanocuboids/nanoplates prepared by combustion synthesis route. In depth characterization study revealed broad spectrum UV–Vis absorption, large interfacial contact, improved charge carrier separation and mobility and a longer excited state life time (4.7 ns) for the ISxBFO heterostructure materials. The integration of In2S3 with Bi2Fe4O9 strongly boosts the optoelectrical and photocatalytic property of pristine Bi2Fe4O9. The ISxBFO heterostructure material exhibited enhanced photocatalytic efficiency for aqueous phase degradation of sulfamethoxazole antibiotics (kapp = 0.06 min−1) and phenyl urea herbicides (kapp = 0.028 min−1) with reaction rates 3–8 times higher than the pure BFO component. The MTT assay experiments confirmed non-cytotoxic nature of treated sulfamethoxazole and diuron solutions. The composite materials also displayed convincing antibacterial behavior towards toxigenic Vibrio cholerae pathogen. Haemagglutination assay study revealed excellent biocompatibility of the binary composite up to 200 mg L−1. Radical trapping study suggested expeditious generation of •OH and •O2− radicals over the ISxBFO surface which is nearly 3.8 and 2.3 times higher than pure BFO and In2S3 respectively. The occurrence of a direct Z-scheme mechanism is inferred from radical trapping and XPS study which accounted for the improved photocatalytic activity and strong radical generation property of the ISxBFO heterostructure material.

Feasibility of UVC laser-activated persulfate with concentrated beam for micropollutant degradation in water

A novel UV light, UVC laser, was used to activate persulfate (PS) for degrading bisphenol A (BPA) in this study. This new light source can emit concentrated beam, and achieve 74.5% of BPA removal within only 60 s when activating PS. Sulfate radicals (SO4−) and hydroxyl radicals (OH) were identified in the UVC laser/PS system. In the case of the same total irradiance energy, the concentrated beam performed a better removal efficiency of BPA than the diffused beam. Compared with the diffused beam, the steady-state concentrations of SO4− and OH under concentrated beam increased by 26.21% and 361.25%, respectively. In addition, the depth-to-diameter ratio (h/D) of the reaction vessels also had a significant effect on the removal efficiency of BPA and the highest degradation rate obtained at h/D = 0.65. High UVC laser intensity, high PS dosage, and circumneutral pH conditions could promote BPA degradation, whereas the presence of water matrix (including chloride, bromide, bicarbonate, and natural organic matter) exhibited opposite effects. The BPA degradation intermediates in the UVC laser/PS system were identified by LCMS and the BPA degradation pathways were proposed accordingly. This study is the first one illustrating the influence of laser beam types, h/D ratio of the reactor vessel, and water matrix on UVC laser/PS application in water treatment process, which can provide essential knowledge for removing micropollutants in water using the novel UVC laser/PS AOP.