Highly efficient Cu(II) capture by salicylaldoxime functionalized magnetic polydopamine core-shell hybrids: Behavior and mechanism.

Functionalized magnetic nanocomposites were considered as promising adsorbents owing to their abundant functional groups and ease of separation properties. Herein, we combined the solvothermal method with molecular copolymerization to synthesize a salicylaldoxime-grafted magnetic polydopamine (SMP) core-shell hybrid and exploited it for Cu(II) adsorption. The physicochemical properties of SMP were comprehensively studied by SEM, TEM, XRD, FT-IR, TGA, XPS, and VSM measurements. The results manifested that polydopamine acts as a bridge connecting magnetic iron oxide and salicylaldoxime to fabricated core-shell hybrids with rich functional groups. The batch experimental results showed that the Cu(II) adsorption was consumingly pH-reliant behavior, while adsorption data fitted the pseudo-second-order kinetic model and Langmuir isothermal model well, and the adsorption process achieved equilibrium within 60 min. Moreover, SMP exhibited remarkable anti-interference and can be recycled for 5 times with an inconspicuous decrease in adsorption performance. Importantly, salicylaldoxime functionalization endowed SMP with maximum Cu(II) adsorption capacity of 141.24 mg/g at pH 6.0 and 25 °C as compared with pure MP. Based on FT-IR and XPS study, the main adsorption mechanisms were proposed with a synergistic effect including a strong chemical chelation and partial Cu(II) reduction. Importantly, this strategy can be extended to multifunctional magnetic composites for Cu-contaminated wastewater cleanup.

Responses of a polycyclic aromatic hydrocarbon-degrading bacterium, Paraburkholderia fungorum JT-M8, to Cd (II) under P-limited oligotrophic conditions.

For the bioremediation of mixed-contamination sites, studies on polycyclic aromatic hydrocarbon (PAH) degradation or Cd (II) tolerance in bacteria are commonly implemented in nutrient-rich media. In contrast, in the field, inocula usually encounter harsh oligotrophic habitats. In this study, the environmental strain Paraburkholderia fungorum JT-M8 was used to explore the overlooked Cd (II) defense mechanism during PAH dissipation under P-limited oligotrophic condition. The results showed that the growth and PAH degradation ability of JT-M8 under Cd (II) stress were correlated with phosphate contents and exhibited self-regulating properties. Phosphates mainly affected the Cd (II) content in solution, while the cellular distribution of Cd (II) depended on Cd (II) levels; Cd (II) was mainly located in the cytoplasm when exposed to less Cd (II), and vice versa. The unique Cd (II) detoxification pathways could be classified into three aspects: (i) Cd (II) ionic equilibrium and dose-response effects regulated by environmental matrices (phosphate contents); (ii) bacterial physiological self-regulation, e.g., cell surface-binding, protein secretion and active transport systems; and (iii) specific adaptive responses (flagellum aggregation). This study emphasizes the importance of considering culture conditions when assessing the metal tolerance and provides new insight into the bacterial detoxification process of complex PAH-Cd (II) pollutants.

Photo-induced adsorption-desorption behavior of methylene blue on CA-BMO under visible light irradiation.

In this work, the modification of Bi2MoO6 with critic acid (CA-BMO) to achieve enhanced adsorption of methylene blue (MB) solution in dark and desorption under visible light irradiation was reported. The as-prepared materials were synthesized by a hydrothermal method and characterized via SEM, FT-IR, XRD, and XPS techniques. Only 16.5% of 10 mg L-1 MB was removed within 10 min by using 0.5 g L-1 Bi2MoO6, while 92.9% removal of MB could be achieved by using 0.5 g L-1 CA-BMO, which enhanced the adsorption removal by a factor of 4.6. The adsorption capacity for MB was 18.9 mg g-1. Desorption efficiency of MB was only observed in CA-BMO system, and it depends on the wavelength of the light source, pH, and the presence of metal ions. Characterization results suggested that carboxyl groups, which were modified onto the surface of Bi2MoO6, could serve as adsorption sites for MB, and the connections were damaged under light, thus leading to the desorption of MB from the surface of the CA-BMO. This study provides a novel reagent-free desorption strategy for dye recovery without secondary pollution, which facilitates the development and application of Bi-based adsorbent for dye-containing wastewater treatment.

Pollution, Ecological Risk and Source Identification of Heavy Metals in Sediments from the Huafei River in the Eastern Suburbs of Kaifeng, China.

Rivers in urban environments are significant components of their ecosystems but remain under threat of pollution from unchecked discharges of industrial sewage and domestic wastewater. Such river pollution, particularly over the longer term involving heavy metals, is an issue of worldwide concern regarding risks to the ecological environment and human health. In this study, we investigate the long-term pollution characteristics of the Huafei River, an important urban river in Kaifeng, China. River sedimentary samples were analyzed, assessing the degree and ecological risk of heavy metal pollution using the geo-accumulation index and potential ecological risk index methods, whilst Pearson's correlation, principal component and cluster analyses were used to identify the sources of pollution. The results show that heavy metal concentrations are significantly higher than their corresponding fluvo-aquic soil background values in China, and the geo-accumulation indexes indicate that of the eight heavy metals identified, Hg is most prevalent, followed in sequence by Cd > Zn > Cu > Pb > Ni > As > Cr. The potential ecological risk index of the Huafei River is very high, with the potential ecological risk intensity highest in the midstream and downstream sections, where it is recommended that pollution control is carried out, especially concerning Hg and Cd. Long-term sequence analysis indicates that Cu and Pb dropped sharply from 1998 to 2017, but rebounded in 2019, and that Zn shows a continuous decreasing trend. Four main sources for the heavy metal contaminants were identified: Cr, Cu, Ni, Pb, Zn and Hg derived mainly from industrial activities, traffic sources and natural sources; Cd originated mainly from industrial and agricultural activities; whilst As was mainly associated with industrial activities. Thus, special attention should be paid to Hg and Cd, and measures must be taken to prevent further anthropogenic influence on heavy metal pollution.

Dye recovery with photoresponsive citric acid-modified BiOCOOH smart material: Simple synthesis, adsorption-desorption properties, and mechanisms.

Dye recovery is of great significance for a circular economy and sustainable development. However, green recovery strategies without secondary pollution remain a significant challenge. To resolve this issue, a light-responsive smart material (citric acid-modified BiOCOOH (m-BOCH)) was synthesized and applied for dye recovery through adsorption in the dark, and desorption under visible light. With the modification of citric acid, the adsorption level of methylene blue (MB) on m-BOCH (43.4%) was more than six times that of pure BiOCOOH (7.1%). The desorption rate was ∼90% in 120 min under 420 nm light irradiation (there was no desorption for pure BOCH). Further, the adsorption rate was improved to 83.9% and the desorption rate remained stable at an optimal pH of 10.09. Characterization results indicated that carboxyl groups were modified onto the surface of BiOCOOH and served as adsorption sites for MB. Under visible light exposure, the connections between the carboxyl groups and BiOCOOH were damaged, which led to the desorption of MB from the surface of the m-BOCH. The recovered MB exhibited a good staining effect on hepatic stellate cells (HSC) as a fresh dye. The regeneration of m-BOCH was achieved through a moderate hydrothermal process, and the adsorption and desorption capacities were restored to 80.8% and 85.7%, respectively. This research provides a novel environmentally compatible strategy for dye recovery without secondary pollution. This is a very promising treatment technique for dye effluents, which highlights the application of smart materials resource recycling for environmental remediation.

Preparing Pd/Sn modified nickel foam electrode for nitrate removal from aqueous solutions.

Nitrate pollution in ground water and surface water has been becoming a worldwide problem that poses a great challenge to steady water ecosystem and human health. Electrochemical reduction is a promising way to remove nitrate from water because of advantages. We prepared Pd/Sn modified nickel foam (NF) electrode according to a two-step electrodeposition method. The prepared NF-Pd/Sn electrode showed a micromorphology like "Karst Fengcong" with peaks, saddles and nadirs intertwined with each other. Pd0 and Sn0 were detected on the NF-Pd/Sn electrode and the mass ratio of Pd/Sn was 4.3/1. The NF-Pd/Sn electrode showed the highest reaction rate (kobs: 0.543 h-1) and removal efficiency (94%) under the condition of 100 mg N/L, 0.05 mol/L Na2SO4 and -1.6 V vs. Ag/AgCl sat. KCl. The highest N2-selectivity (100%) was reached under the condition of 100 mg N/L, 0.05 mol/L NaCl and -1.6 V vs. Ag/AgCl sat. KCl. The microstructure of NF-Pd/Sn electrode like "Karst Fengcong" could provide large specific surface area and more active sites for nitrate adsorption and electrocatalytic reduction in aqueous solution. The adsorption and the reduction reaction of nitrate on the surface of NF-Pd/Sn could increase the electric current response in the test system.

Removal of Zn2+ from Aqueous Solution Using Biomass Ash and Its Modified Product as Biosorbent.

To study the removal effect of bottom ash of biomass power plants and its modified products on zinc (Zn2+) in aqueous solution, a series of indoor experiments is carried out. The aim of this work is to explore a method to improve the ability of biomass ash to remove Zn2+ from aqueous solution and obtain its adsorption characteristics of Zn2+ in aqueous solution; on this basis, the feasibility of its application in the treatment of Zn2+-contaminated wastewater is analyzed. The mesoporous siliceous material is used to modify the biomass, and the modified material is functionalized with 3-aminopropyltriethoxysilane. The results show that the specific surface area of modified biomass ash is nine times that of the material before modification. The adsorption capacity of Zn2+ on the material increases with the increase of pH, and pH 6 is the optimum pH to remove Zn2+ from the aqueous solution. The Langmuir model and Freundlich model can show better fits for biomass ash and the modified material, respectively. Thermodynamic analysis results show that the adsorption of Zn2+ is spontaneous and endothermic in nature. The adsorption of Zn2+ onto biomass and modified biomass ash follow pseudo-first-order and pseudo-second-order kinetics, respectively.

Estimation of Copper and Cadmium Bioavailability in Contaminated Soil Remediated by Different Plants and Micron Hydroxyapatite.

A three-year in situ remediation experiment was carried out to understand the effect of combined phytoremediation with chemical materials on the bioavailability of heavy metals in soil. Indigenous weed (Setaria pumila), energy plant (Pennisetum sp.), cadmium (Cd)-hyperaccumulator (Sedum plumbizincicola), and copper (Cu)-tolerant plant (Elsholtzia splendens) were used as the phytoremediation plants aided by micron hydroxyapatite (1% wt). The bioavailability of Cu and Cd in soil was evaluated during the three years. The results showed that the four plants combined with micron hydroxyapatite significantly increased soil pH and soil organic carbon (SOC), and decreased Cu and Cd fractions extracted by CaCl2 and diffusive gradients in thin films (DGT) than the untreated soils, respectively. Because of the large biomass, the accumulation of Cu and Cd is the largest in Pennisetum sp. followed by Elsholtzia splendens, Sedum plumbizincicola, and Setaria pumila. The bioavailability of Cu and Cd is significantly negatively correlated with pH, soil organic carbon, available phosphorus, and available potassium. Moreover, the correlation is mainly related to the addition of micron hydroxyapatite. The accumulation of Cu and Cd is the combined action of the soil bioavailability of Cu, Cd, and biomass. Our results suggest that Pennisetum sp. can act as an appropriate remediation plant for phytoremediation aided by amendments.

Amlodipine removal via peroxymonosulfate activated by carbon nanotubes/cobalt oxide (CNTs/Co3O4) in water.

Amlodipine (AML) is an effective drug that has been widely used for hypertension and angina. However, AML is frequently detected in aqueous environments, posing potential risks to human and ecological health. In this study, the degradation of AML via peroxymonosulfate (PMS) activated by CNTs/Co3O4 was investigated. CNTs/Co3O4 was prepared via a facile method, and multiple characterizations suggested that Co3O4 were uniformly dispersed on the surface of MWCNTs-COOH. Experimental results indicated that complete removal of 10 µM AML was achieved within 30 min by using 2 mg/L CNTs/Co3O4 and 4 µM PMS at 25 °C in PBS buffered solution (pH 7.0). The observed pseudo-first-order rate constant was calculated to be 0.1369 min-1. Interestingly, the presence of 100 mM Cl- resulted in a slight enhancement of AML removal rate from 0.0528 to 0.0642 min-1. The addition of 100 mM HCO3-, 5 mg/L Pony Lake fulvic acid (PLFA), or Suwannee River humic acid (SRHA) retarded AML degradation by 15.5, 0.7, and 1.6 times, respectively. As per the quenching experiments, SO4⦁- rather than ⦁OH were verified to be the dominant reactive oxygen species (ROS). Additionally, ten major intermediates were identified using TOF-LC-MS and three associated reaction pathways including ether bond broken, H-abstraction, and hydroxylation were proposed. We outlook these findings to advance the feasibility of organic contaminants removal via CNTs/Co3O4 + PMS systems that have extremely low-level PMS.

Interference of dissolved organic matter and its constituents on the accurate determination of hydrogen peroxide in water.

Hydrogen peroxide (H2O2) is ubiquitous in natural waters, and plays an important role in both biological and chemical processes. This study investigated the influence of dissolved organic matter (DOM) and its substituents on the accurate measurement of H2O2 by peroxidase-mediated depletion of scopoletin fluorescence method which is one of the most widely used methods for the determination of low concentration H2O2 in water. Six DOM and its 24 substituents interfered the determination of H2O2 at environmentally relevant concentration of 200 nM with different levels except 2,6-dimethoxy-1,4-benzoquinone and benzoic acid, which may be associated with origin and types of DOM, and numbers and position of active functional groups in DOM constituents. Each substance concentration and the corresponding decreasing ratio to the measured H2O2 concentration was fitted well to the linear model (R2 > 0.9), and the obtained interfering ratios (k, (mgC L-1)-1), expressing the degree of DOM or its substituents per unit concentration to the measurement of H2O2, were approximate for DOM, but the order of magnitude of k values of DOM constituents took on a large span from 10-3 to 10-7. When DOM levels exceed 0.1 mgC L-1 or its substituent concentration is at nM level (low to 20 nM), the H2O2 content will be underestimated substantially. A quantitative structure-activity relationship model with remarkable stability and strong predictability for the k of DOM substituents to H2O2 measurement was established, and the k was related to the electron transfer capacity, hydrophobicity and stability of these compounds.

Effects of Different Particle Sizes of Hydroxyapatite on the Distribution and Migration of Trace Elements (Copper and Cadmium) in a Smelter-Impacted Soil.

To study the remediation effect of hydroxyapatite with different particle sizes, a field in situ experiment was carried out by adding conventional hydroxyapatite (0.25 mm) and microhydroxyapatite (3 µm) and nanohydroxyapatite (40 nm) to the contaminated soil and planting Elsholtzia splendens. The distribution and migration of copper (Cu) and cadmium (Cd) in soil were investigated after 4 years. The results show that the application of three different particle sizes of hydroxyapatite significantly raise the soil pH, total phosphorus, and soil organic carbon. Moreover, the addition of hydroxyapatite can reduce the EXC fraction of Cu and Cd by 73.7%-80.1% and 20.8%-35.2%, respectively. In addition, the concentrations of Cu and Cd in >2 mm, 0.25-2 mm, 0.053-0.25 mm, and <0.053 mm aggregate are significantly increased. This improvement indicates that there are risks which may cause the increasing of total Cu and Cd in the soil where the pollution sources still exist. Furthermore, the content of soil colloid is significantly increased, and the colloidal Cu and Cd distribution percentage have been significantly increased by 49.9%-120% and 30.3%-181%. This result illustrates that the application of hydroxyapatite may greatly increase the possibility of colloid and dust migration of Cu and Cd.

Assessing the influence of immobilization remediation of heavy metal contaminated farmland on the physical properties of soil.

The potential for negative effects of heavy metal remediation on the ecological environment of soil is an issue of widespread concern. As a basic index of soil moisture and fertility retention capacity, the response of the physical properties of soil to immobilization remediation is therefore extremely important and is the main focus of this study on remediated farmland in the mining area of Tangshi village, Henan province, China. Accordingly, topsoil samples and ring knife samples were collected from five separate farmland plots, four of which had been remediated with the respective soil amendments of 1) nano silica; 2) silicate, phosphate and clay minerals; 3) biochar and organic fertilizer; and 4) biochar and phosphate; whilst for experimental control purposes the 5th plot had no remediation measures. The physical properties of particle composition, bulk density, porosity and aggregate were subsequently determined. The results show that nano silica tends to refine the soil, mainly by significantly reducing the content of sand and increasing the content of silt and clay, but did not change the soil texture type. Furthermore, nano silica can promote the formation of soil macro-aggregates and reduce the content of micro-aggregates. However, the other three amendment compositions show no significant effect on soil particle composition and aggregate content. On the whole, the amendments of the four remediation plots can significantly reduce soil bulk density and increase porosity, thus facilitating soil changes that are more beneficial for crop growth. The results, therefore, go some way into alleviating the concerns surrounding heavy metal remediation and damage to the ecological environment of soil.

Identifying dust as the dominant source of exposure to heavy metals for residents around battery factories in the Battery Industrial Capital of China.

Heavy metals (HMs) are constantly released into the environment during the production and use of batteries. Battery manufacturing has been ongoing for over six decades in the "Battery Industrial Capital" (located in Xinxiang City) of China, but the potential exposure pathways of residents in this region to HMs remain unclear. To clarify the exposure pathways and health risk of human exposure to HMs, hand wipe samples (n=82) and fingernail samples (n=36) were collected from residents (including young children (0-6 years old), children (7-12 years old) and adults (30-60 years old)) living around battery factories. The total concentrations of the target HMs (Zn, Mn, Cu, Pb, Ni, Cr, Cd, Co) in hand wipes ranged from 133 to 8040 µg/m2, and those in fingernails ranged from 9.7-566 µg/g. HM levels in the hand wipe and fingernail samples both decreased with age, and higher HM levels were observed for males than females. The HM composition profiles in these two matrices represented a high degree of similarity, with Zn as the predominant element, and thus, oral ingestion and dermal exposure via dust were expected to be the most important HM exposure pathways for residents in this region. The non-carcinogenic risks (HQs) from dermal and oral ingestion exposure to Cd, Cr, and Pb were higher than those of the other five elements for all three populations, and the HQderm of Cd for young children was 2.1 (HQoral=0.6). Moreover, the hazard index (HI) values of ∑8HMs for young children (HItotal=5.2, HIoral=2.0, HIdermal=3.2) and children (HItotal=1.6, HIoral=1.3, HIdermal=0.3) exceeded the safe threshold (1.0). Therefore, young children and children should be prioritized for protection from HM pollution, and more attention should be paid to young children's dermal exposure to Cd in this region.

Critical effect of iron red pigment on photoaging behavior of polypropylene microplastics in artificial seawater.

Microplastics (MPs) containing chemical additives undergo extensive aging in the environment, but the effect of additives on aging behavior of MPs is not fully understood. This study evaluated the effects of iron red pigment on the photoaging behavior of polypropylene (PP) MPs and the release kinetics of Fe(II) and Fe(III) under simulated sunlight. Based on analyses in surface property and aging products of leachate, the incorporated iron red pigment significantly decreased the photoaging rate of PP MPs. The critical effect mainly depended on the light shielding and the competition of pigment for electrons and reactive oxygen species generated from irradiated MPs. Light irradiation also caused the production of homologous series of organic products containing dicarboxylic acid end groups. Moreover, aging of pigmented MPs enhanced the release of Fe ions in leachates, and the types of released iron ions were different between dark and light conditions, where the iron ion in dark system was mainly as Fe(III), while Fe(II) was the dominant form in light irradiation, since the released Fe(III) reacted with MP-derived organic acids and reactive oxygen species in light condition. The findings highlight the critical role of inorganic pigments in the environmental fate and risk of MPs.

The key role of persistent free radicals on the surface of hydrochar and pyrocarbon in the removal of heavy metal-organic combined pollutants.

We show that persistent free radicals (PFRs) on the surface of biochar can produce hydroxyl radicals (•OH) by catalyzing H2O2 to facilitate the removal of the combined pollutant BPA-Cr(VI). Microstructure characterization showed that the structures of pyrocarbon and hydrochar were significantly different when prepared at different temperatures. As the preparation temperature and preparation time for biochar increased, the concentration of PFRs first increased and then decreased. When biochar, PFRs, and H2O2 were present in the same solution, the single pollutants BPA and Cr(VI) as well as the combined pollutant BPA-Cr(VI) could be removed effectively, with removal rates greater than 90%. However, when PFRs, BPA, H2O2, and Cr(VI) were present in the same solution, Cr(VI) competed with H2O2 for electrons and promoted the removal of BPA. The results of this study could be applied to sludge recycling and be used to develop approaches to catalytically degrade combined pollutants.

One-Step Synthesis of Hierarchical Flower-like SnO2/BiOCOOH Microspheres with Enhanced Light Response for the Removal of Pollutants.

The low separation rate of electron-hole pairs in single-component photocatalysts severely limits their applications for wastewater treatment. For this study, SnO2/BiOCOOH photocatalysts in flower-like microspheres were controllably synthesized via a one-step hydrothermal method and were characterized by various advanced techniques. These SnO2/BiOCOOH nanocomposites demonstrated excellent photocatalytic activities for the degradation of rhodamine B (RhB), titan yellow, and levofloxacin hydrochloride (LVF). Specifically, 98.5% of RhB, 80% of titan yellow, and 85% of LVF were degraded under 5 W LED (λ = 365 nm) light irradiation within 30, 40, and 60 min, respectively. Radical trapping experiments and electron spin resonance results indicated that h+ was the dominant active radical, whereas ·O2- and ·OH played an auxiliary role in the photocatalytic system. Subsequently, a potential photocatalytic mechanism was proposed based on the experimental results.

Singlet oxygen production abilities of oxidated aromatic compounds in natural water.

Singlet oxygen (1O2) is well known to be formed through energy transfer from excited state organic matters to O2, playing an important role in the transformations of contaminants. However, the contribution of small oxidated aromatic compounds (OACs) to the production of 1O2 in surface water is unclear. In this study, 28 OACs were selected to investigate the correlations between their photochemical production abilities of 1O2 and molecular structures. Our results showed that the steady-state concentrations and quantum yields of 1O2 (Φ1O2) generated by OACs were in the range of 7.0 × 10-14-1.4 × 10-12 M and 2.2 × 10-4-4.7 × 10-2, respectively, indicating that the photochemical production abilities of 1O2 by OACs varied greatly with types and positions of functional groups on the molecule. More importantly, the observed photochemical production of 1O2 was most notable in cases of molecules containing -OCH3 group and benzoquinone. A good quantitative structure-property relationship model was established between 1O2 producing ability, energy of the lowest unoccupied molecular orbitals (ELUMO) and the most positive net charge of hydrogen atoms (qH+) of OACs. In addition, the role of 1O2 produced by 2, 6-dimethoxy-1, 4-benzoquinone, the OAC with the highest Φ1O2, in the photodegradation of organic contaminants was validated by the enhanced degradation of atorvastatin under simulated sunlight, suggesting that OACs ubiquitously existed in surface water may greatly affect the fate and ecological risks of organic contaminants.

Efficient removal of triclosan via peroxymonosulfate activated by a ppb level dosage of Co(II) in water: Reaction kinetics, mechanisms and detoxification.

Triclosan (TCS), an extensively used broad-spectrum antimicrobial agent, has raised significant environmental concerns regarding its widespread occurrence in waters. In this study, the removal of TCS in aqueous solution via peroxymonosulfate (PMS) activated by an extremely low-level Co2+ (0.02 µM) was systematically investigated. During preliminary test, TCS (10 µM) was totally degraded in 30 min by using 0.1 µM Co2+ and 40 µM PMS at pH 7.0 with a degradation rate constant of 0.1219 min-1. A first-order apparent degradation rate of TCS was found with respect to the PMS concentrations. At extremely low dosage of Co2+ (0.02 µM), the presence of NO3-, HCO3-, PLFA, and SRHA within test concentrations significantly inhibited TCS removal, while a dual effect of Cl- on the degradation rate of TCS was observed. The quenching experiments verified that SO4- was the dominant reactive oxygen species (ROS) rather than OH. Six major intermediates were identified using TOF-LC-MS, based on which we proposed three associated reaction pathways including hydroxylation, ether bond breakage, and dechlorination. Toxicity predictions by ECOSAR software exhibited aquatic toxicity reduction of TCS after Co2+/PMS treatment. We outlook these findings to advance the feasibility of organic contaminants removal via Co2+/PMS system with Co2+ at extremely low levels.

Smart Removal of Dye Pollutants via Dark Adsorption and Light Desorption at Recyclable Bi2O2CO3 Nanosheets Interface.

The adsorbents for water treatment and purification are commonly not recyclable because of the lack of a reagent-less "switch" to readily release the adsorbed compounds. Herein, the interface of Bi2O2CO3 (BOC) nanosheets is designed, synthesized, and modified with citric acid, namely, modified Bi2O2CO3 (m-BOC). The m-BOC is able to selectively adsorb methylene blue (MB) in the dark and the adsorbed MB could be released in the light from m-BOC without the addition of any chemicals. The adsorption mechanism is attributed to the electrostatic attraction between positively charged MB and the negatively charged surface of m-BOC. In contrast, the desorption of MB has resulted from the photo-induced charge redistribution on the surface of m-BOC, which unlocks the coordination bond between m-BOC and the carboxylic group. As a result, BOC is recycled. Such a mechanism was verified by both experimental investigation and DFT calculation. This work provides a promising interfacial engineering strategy for the remediation of dye-polluted water and smart separation in chemical engineering.

A novel visible light controllable adsorption-desorption system with a magnetic recyclable adsorbent.

Convenient and energy-efficient desorption or regeneration processes are prerequisites for the development of an ideal adsorbent. For this work, a novel magnetic adsorbent (citric acid/Bi2O2CO3/Fe3O4) was controllably synthesized via a facile hydrothermal method. The as-prepared materials demonstrated the excellent adsorption of methylene blue (MB), where ~70% of the MB was absorbed within 10 min. Interestingly, the desorption process could be triggered by visible light irradiation, and 99% of the absorbed MB was released into solution within 4 h. Further, the magnetic materials could be conveniently recovered using a magnet and regenerated via a model hydrothermal process. Even after two regeneration cycles, approximately 60% adsorption and 63% desorption abilities were retained, which suggested strong potential for the recyclability of these materials.