Acetaminophen (ACE) is commonly used in analgesic and antipyretic drug, which is hardly removed by traditional wastewater treatment processes. Herein, amorphous Co(OH)2 nanocages were explored as peroxymonosulfate (PMS) activator for efficient degradation of ACE. In the presence of amorphous Co(OH)2 nanocages, 100% of ACE removal was reached within 2 min with a reaction rate constant k1 = 3.68 min−1 at optimum pH 5, which was much better than that of crystalline β-Co(OH)2 and Co3O4. Amorphous materials (disorder atom arrangement) with hollow structures possess large specific surface area, more reactive sites, and abundant vacancies structures, which could efficiently facilitate the catalytic redox reactions. The radicals quenching experiment demonstrated that SO4− radicals dominated the ACE degradation rather than OH radicals. The mechanism of ACE degradation was elucidated by the analysis of degradation intermediates and theoretical calculation, indicating that the electrophilic SO4− and OH tend to attack the atoms of ACE with high Fukui index (f −). Our finding highlights the remarkable advantages of amorphous materials as heterogeneous catalysts in sulfate radicals-based AOPs and sheds new lights on water treatment for the degradation of emerging organic contaminants.
This study reports the different degradation mechanisms of carbamazepine (CBZ) and diclofenac (DCF) by single-atom Barium (Ba) embedded g-C3N4. Single-atom Ba is anchored onto g-C3N4 by forming ionic bond with triazine ring, thus greatly enhances the photocatalytic activity with an atom ratio of 1.78%. CBZ undergoes a typical photocatalysis mechanism, while DCF is degraded via a photosensitization-like process, which does not need band gap excitation of photocatalyst. By means of Density Functional Theory (DFT) calculation, the selectivity is found to be related with the different valence excitation modes of CBZ and DCF. Specifically, CBZ undergoes a local excitation, which does not obviously affect molecular configuration. In contrast, DCF undergoes a charge transfer excitation, which significantly changes the reactive sites distribution and facilitates photosensitization-like degradation. Due to the different degradation mechanism, the effects of pH, co-existed anions, and water matrix are also different. Since photosensitization-like mechanism does not rely on photo-generated holes mediated oxidation, the degradation efficient of DCF shows higher anti-interference capacity in real water.
Covalent organic frameworks (COFs) have great application potentials in photocatalytic water treatment. By using p-phenylenediamine with different numbers and locations of heterocyclic nitrogen atoms as a precursor, five types of COFs with different nitrogen positions were synthesized. We found that Cr(VI) photoreduction,Escherichia coli inactivation, and paracetamol degradation by COFs were heterocyclic nitrogen location-dependent. Particularly, the photocatalytic performance for all three tested pollutants by five types of COFs followed the order of the best performance for COF-PDZ with two ortho position heterocyclic N atoms, medium for COF-PMD with two meta position heterocyclic N atoms, and COF-PZ with two para position heterocyclic N atoms, and COF-PD with a single heterocyclic N atom, the worst performance for COF-1 without a heterocyclic N atom. Compared to the other COFs, COF-PDZ contained improved quantum efficiency and thus enhanced generation of electrons. The lower energy barriers and larger energy gaps of COF-PDZ contributed to its improved quantum efficiencies. The stronger affinity to Cr(VI) with lower adsorption energy of COF-PDZ also contributed to its excellent Cr(VI) reduction performance. By transferring into a more stable keto form, COF-PDZ showed great stability through five regeneration and reuse cycles. Overall, this study provided an insight into the synthesis of high-performance structure-dependent COF-based photocatalysts.
PDINH/MIL-88A(Fe) composites (PxMy) were fabricated from MIL-88A(Fe) and perylene-34,910-tetracarboxylic diimide (PDINH) via facile ball-milling strategy. The optimum P25M175 exhibited outstanding degradation performance toward chloroquine phosphate (CQ) by activating peroxydisulfate (PDS) under low power LED visible light. The synergistic effects of photocatalytic activations of PDS via the direct electron transfer PDS activation over P25M175 and indirect electron transfer PDS activation over pristine MIL-88A contributed to the boosted CQ degradation efficiency. The active species capture experimental data and electron spin resonance (ESR) determinations revealed that both active radicals (like SO4−, OH, O2−, h+) and nonradical singlet oxygen (1O2) participated in the CQ decomposition. The CQ degradation pathways and the toxicity evaluation of the intermediates were proposed based on LC–MS determination and DFT calculation. Also, P25M175 demonstrated good reusability and stability. The findings within this work offered deep insights into the mechanisms of organic pollutants degradation via photocatalysis-activated SR-AOP over Fe-MOF photocatalyst.
Perfluorooctane sulfonate (PFOS) has drawn increasing attention due to its omnipresence and adverse health effects. We prepared a new adsorptive photocatalyst, Ga/TNTs@AC, based on activated carbon and TiO2, and tested the adsorption and subsequent solid-phase photodegradation of PFOS. Ga/TNTs@AC showed faster adsorption kinetics and higher affinity for PFOS than the parent AC, and could degrade 75.0% and mineralize 66.2% of pre-sorbed PFOS within 4-h UV irradiation. The efficient PFOS photodegradation also regenerates Ga/TNTs@AC, allowing for repeated uses without invoking chemical regenerants. The superior photoactivity is attributed to the oxygen vacancies, which not only suppressed recombination of the e−/h+ pairs, but also facilitated O2− generation. Both h+ and O2− played critical roles in the PFOS degradation, which starts with cleavage of the sulfonate group and converts it into PFOA that is then decarboxylated and defluorinated following the stepwise defluorination mechanism. Ga/TNTs@AC holds the potential for more cost-effective PFOS degradation.
Quantitative identification on reactive sites of target organic molecule during photocatalysis can help to get deep insight into the pollutant degradation pathway and energy evolution process. In this study, a new class of silica aerogel supported TiO2 (TiO2/SiO2) photocatalysts were fabricated via a two-step approach, and applied for adsorption and photocatalytic degradation of phenanthrene. Anatase crystalline structure was formed upon calcination at 400 and 600 °C, while mixed crystal interphases of anatase and rutile were generated at 800 °C (anatase:rutile = 0.67:0.33). The higher calcination temperature resulted in better crystallinity of TiO2, higher photocatalytic activity, and reduced adsorption affinity toward phenanthrene. TiO2/SiO2-800 (TiO2/SiO2 calcined at 800 °C) showed minimal phenanthrene uptake ( 5.2%) but the strongest photocatalytic activity, and it was able to completely degrade phenanthrene within 3 h. The SiO2 aerogel component in the composite enabled the pre-concentration of phenanthrene on the photoactive sites, while the nanoscale mixed-phases of anatase and rutile of TiO2/SiO2-800 act as an efficient transfer medium for photo-induced charge carriers. Moreover, the formed Ti–O–Si linkage in TiO2/SiO2-800 induced formation of Ti3+ under solar light irradiation, promoting photoexcited electron trap and separation of electron-hole pairs. Based on the degraded phenanthrene intermediates/products, theoretical calculations according to the density functional theory (DFT) reveal that the atoms of phenanthrene with high electrophilic Fukui index (f -) are the most reactive sites towards the radicals. Potential energy surface profile for phenanthrene degradation further reveals the intermediates energy evaluation via radicals attack.
A highly solar active AgBr/h-MoO3 composite was constructed by a facile precipitation method, and the charge separation tuning was achieved by photoreduction of AgBr. The photoreduced Ag0 on AgBr/h-MoO3 acted as charge transfer bridge to form Z-scheme heterostructure, while the high degree of Ag reduction converted the material into type-II heterostructure. The synthesized optimal material promoted charge separation and visible light activity due to the incorporation of highly solar active AgBr, which showed ca. 2 times activity on trimethoprim (TMP) degradation than h-MoO3. The contribution of reactive species on TMP degradation followed the order of O2− > 1O2 > h+, which agree well with the proposed charge separation mechanism. The photocatalytic degradation mechanism of TMP was proposed based on the radical quenching, intermediate analysis and DFT calculation. The toxicity analysis based on QSAR calculation showed that part of the degradation intermediates are more toxic than TMP, thus sufficient mineralization are required to eliminate the potential risks of treated water. Moreover, the material showed high stability and activity after four reusing cycles, and it is applicable to treat contaminants in various water matrix. This work is expected to provide new insight into the charge separation tuning mechanism for the AgX based heterojunction, and rational design of highly efficient photocatalysts for organic contaminants degradation by solar irradiation.
Degradation pathway is important for the study of carbamazepine (CBZ) removal in advanced oxidation processes (AOPs). Generally, degradation pathways are speculated based on intermediate identification and basic chemical rules. However, this semiempirical strategy is sometimes time-consuming and baseless. To improve the situation, a mini meta-analysis was first conducted for the degradation pathways of CBZ in AOPs. Then, the rationality of the pathways was analyzed by Density Functional Theory (DFT) calculation. Results show that the degradation pathways of CBZ in various AOPs has high similarity, and the reactive sites predicted by Fukui function fitted well with the data retrieved from literatures. In addition, molecule configuration of degradation intermediates was found to play a very important roles on degradation pathway. The study reveals that computational chemistry is a useful tool for degradation pathway speculation in AOPs.
Herein, a silicate-enhanced flow-through electro-Fenton system with a nanoconfined catalyst was rationally designed and demonstrated for the highly efficient, rapid, and selective degradation of antibiotic tetracycline. The key active component of this system is the Fe2O3 nanoparticle filled carbon nanotube (Fe2O3-in-CNT) filter. Under an electric field, this composite filter enabled in situ H2O2 generation, which was converted to reactive oxygen species accompanied by the redox cycling of Fe3+/Fe2+. The presence of the silicate electrolyte significantly boosted the H2O2 yield by preventing the O–O bond dissociation of the adsorbed OOH*. Compared with the surface coated Fe2O3 on the CNT (Fe2O3-out-CNT) filter, the Fe2O3-in-CNT filter demonstrated 1.65 times higher kL value toward the degradation of the antibiotic tetracycline. Electron paramagnetic resonance and radical quenching tests synergistically verified that the dominant radical species was the 1O2 or HO· in the confined Fe2O3-in-CNT or unconfined Fe2O3-out-CNT system, respectively. The flow-through configuration offered improved tetracycline degradation kinetics, which was 5.1 times higher (at flow rate of 1.5 mL min–1) than that of a conventional batch reactor. Liquid chromatography–mass spectrometry measurements and theoretical calculations suggested reduced toxicity of fragments of tetracycline formed. This study provides a novel strategy by integrating state-of-the-art material science, Fenton chemistry, and microfiltration technology for environmental remediation.
The potential exposure of titanate nanotubes (TNTs) to wildlife and humans may occur as a result of increased use and application as functional nanomaterials. However, there is a dearth of knowledge regarding the pathways of uptake and excretion of TNTs and their toxicity in cells. In this study, three strains of the Tetrahymena genus of free-living ciliates, including a wild type strain (SB210) and two mutant strains (SB255: mucocyst-deficient; NP1: temperature-sensitive “mouthless’’), were used to study the pathways of uptake and excretion and evaluate the cytotoxicity of TNTs. The three Tetrahymena strains were separately exposed to 0, 0.01, 0.1, 1 or 10 mg/L of TNTs, and cells were collected at different time points for quantification of intracellular TNTs (e.g., 5, 10, 20, 40, 60, 90 and 120 min) and evaluation of cytotoxicity (12 and 24 h). TNT contents in NP1 and SB255 were greater or comparable to the contents in SB210 while exposure to 10 mg/L TNTs in 120 min. Furthermore, exposure to 10 mg/L TNTs for 24 h caused greater decreases in cell density of NP1 (38.2 %) and SB255 (36.8 %) compared with SB210 (26.5 %) and upregulated the expression of caspase 15 in SB210. Taken together, our results suggested that TNT uptake by pinocytosis and excretion by exocytosis in Tetrahymena, and the exposure could cause cytotoxicity which can offer novel insights into the accumulation kinetics of nanotubes and even nanomaterials in single cell.
In this study, we designed an integrated electrochemical filtration system for catalytic activation of peroxymonosulfate (PMS) and degradation of aqueous microcontaminants. Composites of carbon nanotube (CNT) and nanoscale zero valence copper (nZVC) were developed to serve as high-performance catalysts, electrode and filtration media simultaneously. We observed both radical and nonradical reaction pathways, which collectively contributed to the degradation of model pollutants. Congo red was completely removed via a single-pass through the nZVCCNT filter (τ <2 s) at neutral pH. The rapid kinetics of Congo red degradation were maintained across a wide pH range (from 3.0–7.0), in complicated matrixes (e.g., tap water and lake water), and for the degradation of a wide array of persistent organic contaminants. The superior activity of nZVCCNT stems from the boosted redox cycles of Cu2+/Cu+ in the presence of an external electric field. The flow-through design remarkably outperformed the conventional batch system due to the convection-enhanced mass transport. Mechanism studies suggested that the carbonyl group and electrophilic oxygen of CNT served as electron donor and electron acceptor, respectively, to activate PMS to generate •OH and 1O2 via one-electron transport. The electron-deficient Cu atoms are prone to react with PMS via surface hydroxyl group to produce reactive intermediates (Cu2+-O-O-SO3−), and then 1O2 will be generated by breaking the coordination bond of the metastable intermediate. The study will provide a green strategy for the remediation of organic pollution by a highly efficient and integrated system based on catalytic oxidation, electrochemistry, and nano-filtration techniques.
A highly solar active nanocomposite with sheet-like WO3 skeleton and evenly loaded TiO2 and carbon quantum dots (CQDs) was synthesized by facile hydrothermal-calcining process, which showed 3.1- and 46.6- times activity on antibiotic (cephalexin) degradation than TiO2 and WO3, respectively. The construction of TiO2/WO3 heterojunction narrowed the band gap and facilitated the electrons-holes separation. The π conjugated CQDs was found to further improve the charge separation and extend the visible light response by photosensitization. However, the promoted charge separation predominantly contributed to the improved photocatalytic activity. The contributions of detected reactive species follows the order of: O2–>1O2>OH>h+. The cephalexin degradation mechanism and pathway were proposed based on DFT (density functional theory) calculation and experimental analysis. The photocatalytic mineralization efficiency can reach 92.4% in 4 h, indicating the efficient reduction of ecotoxicity of cephalexin and its intermediates. This new composite proved to have great potentials for emerging contaminants degradation in water.
In present study, we fabricated sulfhydryl modified covalent organic frameworks (COF-‒SH) through one-step reaction for the removal of Hg(II) from water. Different techniques were employed to characterize the fabricated COFs. We find that COF-‒SH exhibits great adsorption capacity (1283 mg/g) towards Hg(II), which is over 25 times higher than that of COF-1 without ‒–SH (53.1 mg/g). COF‐SH has fast adsorption kinetics with the removal of 95% of 1000 μg/L Hg(II) within 30 min and over 99% after 2 h. Under a wide pH range (from 4 to 9), COF-‒SH exhibits high removal efficiencies (>99%). Moreover, COF‐SH can selectively adsorb Hg(II) in the presence of other metal cations up to 1000 μg/L. X-ray photoelectron spectroscopy analysis reveals the presence of high affinity between thiol-S atom and Hg(II), which is also responsible for the high selectivity towards Hg(II) compared with other cations. Because of the transfer from enol form to keto form during synthesis, COF‐SH exhibit remarkable stability during 10-cycle regeneration and reuse test. During utilization in wastewater extracted from Hg contaminated sludge, COF-‒SH displays high Hg(II) removal efficiency (>95%) under multiple coexisting ions conditions. The results suggest that COF-‒SH have great potential for Hg(II) removal from water under complex conditions.
A novel solar active AgBr/BiOBr/TiO2 catalyst was synthesized by a facile coprecipitation method for solar-driven water remediation. The synthesized material composed of flower-like TiO2 nanoparticles loaded on BiOBr nanosheets and with homogeneous surface distributed Ag/AgBr nanoparticles. The internal electric field between BiOBr/TiO2 heterojunction greatly facilitated the charge carrier migration; the introduction of narrow band gap semiconductors (AgBr and BiOBr) promoted the visible light adsorption; and the Ag/AgBr nanoparticles acted as photosensitizer to further improve the light utilization. The new material showed 7.6- and 4.0-times activity of pure TiO2 and BiOBr under solar light, and the contribution of reactive species on anthracene degradation followed the order of h+ >O2•−> •OH. The degradation mechanism and pathway were proposed based on intermediates analysis and DFT calculation. The QSAR analysis revealed that the environmental risks of contaminants were greatly reduced during the photocatalysis process but some intermediates were still toxic. The high photocatalytic activity, stability and adaptability all indicated that this new material owns great application potential for cost-effective photocatalytic remediation of persistent organic contaminants under solar light.
Herein, through supramolecular gel assisted pre-configuration, a novel bamboo-like porous graphitic carbon nitride (g-C3N4) deposited with single-atom Fe was successfully prepared and used for sulfite (S(IV)) activation. Unexpectedly, owing to the presence of single-atom Fe, hybrid material with only 2.5‰ of Fe exhibited 16 times higher S(IV) activation efficiency for diclofenac removal than pure g-C3N4 under visible light irradiation. Moreover, a synergetic effect of Fe and g-C3N4 was found to play the dominate role, and the synergetic factor was calculated to be 0.84. The synergetic mechanism mainly related to the generation of surface Fe-S(IV) complex, which could be affected by S(IV) species or the presence of H2PO4−. DCF removal was significantly enhanced at alkaline condition, but the enhancement was mainly attributed to photocatalysis but not synergetic effect. Decarboxylation, hydroxylation, chlorine abstraction and cleavages at bridging N atom were the main degradation pathways of DCF, which agreed well with Fukui index prediction. The toxicity of DCF was alleviated during the degradation process through successful mineralization of chlorine atoms.
V-Fe concentrate ore was applied to activate peroxydisulfate (PDS) for carbamazepine (CBZ) degradation. The excellent performance of V-Fe concentrate ore was mainly ascribed to the quick electron transfer from surface ≡V(III) and ≡V (IV) to ≡Fe(III) for ≡Fe(II) regeneration, which was confirmed by XPS and XAS analyses. This accelerated ≡Fe(II) regeneration could thus lead to quick formation of HO, SO4−, O2− and effective degradation of CBZ. The degradation rate of CBZ could be also expressed by a kinetic model, i.e., −d[CBZ]/dt = (0.83 mM-0.55 min-1(g/L)-0.65) [CBZ]0.29[PDS]1.26[V-Fe]0.65. Combined with the measured intermediates and the results of DFT calculation, CBZ degradation pathway was proposed systematically. Moreover, this catalyst displayed excellent recyclability and general applicability for a broad substrate scope. This study suggests low valent vanadium makes crucial contributions to the high activity of V-Fe-based catalysts, and improves the understanding of electron transfer mechanism between V and Fe in PDS activation process.
Pharmaceuticals and personal care products (PPCPs) are of great concern due to their increasing health effects, so advanced treatment technologies for PPCPs removal are urgently needed. In this study, titanate nanotubes decorated Co(OH)2 hollow microsphere (CoM/TNTs) composites were synthesized by a two-step solvothermal method, and used to activate peroxymonosulfate (PMS) through heterogenous catalysis for acetaminophen (ACE) degradation in water. The optimum material (CoM/TNTs0.5) activated PMS system exhibited high ACE removal efficiency and quick kinetic, as 93.0% ACE was degraded even within 10 min. The two components in CoM/TNTs showed a synergetic effect on PMS activation for radicals production: Co(OH)+ from CoM was the primary active species to active PMS, while TNTs could offer abundant –OH groups for Co(OH)+ formation. Density functional theory (DFT) calculation further interpreted the mechanism of Co(OH)+ for PMS activation by means of reaction potential energy surface (PES) analysis. Both the scavenger quenching tests and electron paramagnetic resonance analysis revealed that the sulfate radical (SO4-·) played a dominant role in ACE degradation. Moreover, DFT calculation also suggested that the ACE atoms with high Fukui index (f -) represented the active sites for electrophilic attack by SO4-·. The toxicity analysis based on quantitative structure-activity relationship (QSAR) verified the reduced toxicity of transformation products. Furthermore, CoM/TNTs also had good reusability and stability over five cycles. This work provides deep insights into the reaction mechanisms of radical production and organics attack in cobalt-based PMS activation system.
Bifunctional Bi12O17Cl2/MIL-100(Fe) composite (BMx) was firstly constructed via facile ball-milling method. The optimal BM200 was highly efficient for Cr(VI) sequestration and activation of persulfate (PS) for bisphenol A (BPA) decomposition under white light illumination, which was much more remarkable than the pristine MIL-100(Fe) and Bi12O17Cl2, respectively. Furthermore, the photocatalytic reduction efficiency can be significantly improved via the addition of some green small organic acids (SOAs). As well, the BPA degradation can be achieved over an extensive initial pH range of 3.0–11.0. When the PS concentration increased to more than 2.0 mM, the BPA degradation efficiency decreased due to the SO4−• self-scavenging effect. It was also found that the co-existence of inorganic anions like H2PO4−, HCO3−, SO42−, Cl− and NO3− could decelerate the BPA degradation. The excellent photocatalytic Cr(VI) reduction and persulfate activation performances originated from both MIL-100(Fe) with excellent PS activation ability and Bi12O17Cl2 with a favorable band position, which not only enabled the efficient separation of charges but also accelerated the formation of SO4−• radicals. The BM200 displayed prominent stability and recyclability. More importantly, the credible degradation pathway was proposed based on UHPLC-MS analysis and DFT calculation. This research revealed that the Fe-based MOFs/bismuth-rich bismuth oxyhalides (BixOyXz, X = Cl, Br and I) composites possessed great potential in wastewater remediation.
Developing efficient pharmaceuticals and personal care products (PPCPs) degradation technologies is of scientifical and practical importance to restrain their discharge into natural water environment. This study fabricated and applied a composite material of amorphous MnO2 nanoparticles in-situ anchored titanate nanotubes (AMnTi) to activate peroxymonosulfate (PMS) for efficient degradation and mineralization of carbamazepine (CBZ). The degradation pathway and toxicity evolution of CBZ during elimination were deeply evaluated through produced intermediates identification and theoretical calculations. AMnTi with a composition of (0.3MnO2)•(Na1.22H0.78Ti3O7) offered high activation efficiency of PMS, which exhibited 21- and 3-times degradation rate of CBZ compared with the pristine TNTs and MnO2, respectively. The high catalytic activity can be attributed to its unique structure, leading to a lattice shrinkage and small pores to confine the PMS molecule onto the interface. Therefore, efficient charge transfer and catalytic activation through MnOTi linkage occurred, and a MnTi cycle mediating catalytic PMS activation was found. Both hydroxyl and sulfate radicals played key roles in CBZ degradation. Theoretical calculations, i.e., density functional theory (DFT) and computational toxicity calculations, combined with intermediates identification revealed that CBZ degradation pathway was hydroxyl addition and NC cleavage. CBZ degradation in this system was also a toxicity-attenuation process.