Heavy Metal Ions Cr Research Articles

Mott–Schottky heterostructural TiO2@Ag@AgBr nanohybrids for efficient photocatalytic degradation of Cr (VI) and enhanced on-site SERS detection

In the study, a novel ternary composite TiO2@Ag@AgBr was successfully prepared by surface modification of complete Ag layer and AgBr particles for photocatalytic degradation of representative heavy metal ions Cr (VI) and on-site Surface-enhanced Raman spectroscopy (SERS) detection of the Cr (VI) reduction process. The Mott–Schottky heterojunction contained structure exhibited remarkable photocatalytic ability for heavy metal ions Cr (VI) by tuning the ratio of Ag and AgBr, which could reduce Cr (VI) ions within 30 min and the reaction rate constant is 0.12 min−1. The remarkable photo-reduction performance is attributed to synergistic effect among the various components: the AgBr decorated on the surface of TiO2@Ag could significantly enhance the absorption of visible light and generate numerous photoexcited electrons and holes. Furthermore, the complete Ag layer was constructed on the TiO2 microspheres surface to form heterojunctions in the photocatalytic system by in-situ deposition of AgNO3. Mott–Schottky junctions formed between AgBr/Ag and Ag/TiO2 interface which could extend the charge transfer pathway and facilitate separation of photoexcited electrons and holes. The plasmonic metal layer of nano Ag could generate significant surface plasmon resonance (SPR) effect which not only enhanced the absorption of visible light but also exhibited remarkable SERS effect for probe molecules. And an amazing detection limit of 1 × 10–10 M could be obtained when using crystal violet (CV) as probe molecules. In addition, the SERS substrates exhibited significant linear relationship between concentration and SERS signal intensity which ensures the accuracy of quantitative analysis and monitoring photoreduction process. The substrates have good cycling stability, enabling it to be reused for SERS detection many times. Thus, the excellent photocatalytic and SERS performance of Mott–Schottky hetero-structural TiO2@Ag@AgBr substrates shows great potential toward rapidly photocatalytic removal Cr (VI) ions and SERS on-site detection reduction process of Cr (VI) in waste water, which is of great significance to environmental protection and ecological restoration.

Porous carbon nanofiber/porphyrin-based metal organic frameworks/TiO2 nanoparticles ternary materials for selective detection and photoreduction of Cr(Ⅵ)

For the heavy metal ion Cr(Ⅵ), which is widely present in wastewater with acute toxicity, mutagenicity and carcinogenicity, we successfully constructed a ternary material of PCNFs/CuMOF/TiO2 for rapid detection and photoreduction of Cr(Ⅵ). The material has obvious advantages: on the one hand, ZIF-8/polyacrylonitrile (PAN) nanofibers and their derived porous carbon nanofibers (PCNFs) were synthesized by electrospinning and high temperature carbonization, which provided a loading platform for CuMOF and TiO2, effectively inhibited the agglomeration of CuMOF and TiO2, and ensured the exposure of active sites. Meanwhile, its excellent conductivity can promote the effective migration of photogenerated carriers in the photocatalytic process. On the other hand, CuMOF constructed with tetra-carboxyphenylporphyrin (TCPP) as the linking arm and Cu(NO3)2·3 H2O as the metal node was directly loaded on the surface of porous carbon nanofibers (PCNFs), and then TiO2 nanoparticles were introduced by hydrothermal method. CuMOF ensures the responsiveness of the composite to visible light. Moreover, the energy level structure of TiO2 matches with CuMOF, which effectively inhibits the recombination of photogenerated electron-hole pairs (e--h+). The results show that the colorimetric detection of Cr(Ⅵ) was achieved by using 3,3′,5,5′-tetramethylbenzidine (TMB) as the sensing probe. The method was highly selective for Cr(Ⅵ) ions with a limit of detection (LOD) of 24.1 nM. Encouragingly, PCNFs/CuMOF/TiO2 was further used as a photocatalyst. The reduction rate of Cr(Ⅵ) under visible light irradiation is 96.1 % in 60 min. The active species trapping experiments confirm the key role of e- photocatalytic reduction, upon which a possible photocatalytic mechanism is proposed. The degradation rate of Cr(Ⅵ) is still 86.4 % after the five times cycle, and the good stability and reproducibility allow it to be used as a potential green photocatalyst for the conversion of Cr(Ⅵ) to Cr(Ⅲ).

Heterogeneous single-atom doped 2D-layered graphitic carbon nitride electrocatalyst for oxygen evolution reaction and removal of toxic heavy metal ion Cr from Wastewater

The 2D-layered graphitic carbon nitride (gCN) has been a well-known electro-photocatalyst to have wide applications in energy storage, energy evolution, and environmental remediation. The physicochemical properties of the bulk, O-doped (O-gCN), and hetero atom are compared, which is further utilized as an electrocatalyst for the oxygen evolution reactions (OER) process. The prepared nanosheets exhibited a layered structure with a uniform porous nature. Moreover, the forbidden energy bandgap (Eg) of 1.7 eV is observed, which is lower than bulk and O-doped gCN. The heteroatom BO-gCN nanosheets have higher OER activity compared to other samples and benchmark catalysts. The BO-gCN nanosheets exhibit a lower overpotential and Tafel potential of 240 mV and 207 mV/dec, respectively. Effects of various operating parameters such as photocatalyst dosage and solution pH are investigated. The photocatalytic removal results exhibited BO-gCN can be a robust and effective catalyst for the removal of Cr ions in environmental remediation.

Enhancing catalytic performance of TiO2/P-doped C3N4 composite via preferentially bonded P-O-Ti

Optimizing photocatalyst structure at the atomic level is a crucial challenge in improving photocatalytic performance. Herein, a series of TiO2/P-doped C3N4-pinned composites have been synthesized to optimize photocatalyst structure at the atomic level. Among the nonmetals (P, C, and N) in P-doped C3N4 (CN-P), TiO2 preferentially bonds with P to form stable P-O-Ti chemical bonds that can act as efficient carrier transfer channels. Comprehensive correlations between P-O-Ti bond features, defects, carrier kinetics, and photocatalytic activity have been studied theoretically and experimentally. Photocurrent-time curves and distribution of relaxation times analysis reveals that preferentially bonded P-O-Ti improves carrier separation and transfer. The special P-O-Ti interface bonds endows composites TiO2/P-doped C3N4 with multifunctional photocatalysis properties, i.e., hydrogen production (815 µmol g−1 h−1), and completely reducing heavy metal ions Cr (VI) (10 min ) under visible light (λ > 400 nm) irradiations, which outperforms most of existing CN-P and TiO2 composite catalysts, as well as excellent degradation performance for organic contaminants. More importantly, the composite with optimal composition shows a superior stability and repeatability in ten cycles of testing. These findings provide valuable hints in optimizing photocatalyst structure at the atomic level for enhancing carrier dynamics and improving photocatalytic performance necessary for applications under visible light.

Synthesis and characterization of Ppy/Bi2MoO6 heterojunction with enhanced photodegradation efficiency of Cr(VI)

To effectively degrade heavy metal ion Cr(VI), Bi2MoO6 and Ppy/Bi2MoO6 composite photocatalyst were successfully prepared using simple solvothermal and in-situ polymerization deposition methods. Compared with pure Bi2MoO6, the Ppy/Bi2MoO6 exhibited dramatically improved photocatalytic activity. The larger specific surface area and higher electronic conductivity of Ppy improve the photocatalytic performance of Bi2MoO6. Especially when the addition amount of Ppy is 0.5 mmol, the degradation rate of 5 mg/L Cr(VI) solution can reach 93.4% after 70min of illumination, and the corresponding degradation reaction rate constant is 0.03893min−1, which is 3.32 times higher than that of pure Bi2MoO6 and 12.56 times higher than that of pure Ppy. At the same time, the photocatalytic activity of the 0.5Ppy/Bi2MoO6 photocatalyst was 0.33mg/(g·min), and the composite photocatalyst exhibited excellent photocatalytic activity. In addition, the deposition of Ppy narrowed the band gap of the composite material and broadened the light absorption range. The electrochemical impedance spectra demonstrated that the introduction of Ppy nanoparticles on the surface of Bi2MoO6 could effectively accelerate the separation of electron and hole pairs. Analyzing the catalytic mechanism, it is speculated that a traditional type-II or Z-scheme heterojunction may have been formed between Ppy and Bi2MoO6, establishing a photo-generated electron and hole transfer channel, hindering the recombination of charge carriers and improving the separation rate, and facilitating the photocatalytic reaction. This work indicated that construction Ppy/Bi2MoO6 composite photocatalysts is an effective approach to improve photocatalytic activity for degradation of Cr(VI).

Sulfur-doped Sb4Mo10O31 bimetallic sulfur-oxide catalyst for highly efficient reduction of toxic organic and hexavalent chromium under dark

Sulfur-doped Sb4Mo10O31 bimetallic sulfur-oxide catalyst (labeled as SbMoSO) was synthesized by thermal hydrolysis using different amounts of S precursor CH3CSNH2 (TAA). SbMoSO catalysts for reducing toxic organic pollutants (4-nitrophenol (4-NP)), organic dyes (Methyl orange (MO), Methylene blue (MB), Rhodamine B (RhB)), and heavy metal ions Cr(VI) in water were studied. SbMoSO-2 catalyst showed the best catalytic performance. 10 mg SbMoSO-2 ultimately reduced 100 mL of 10 ppm 4-NP within 10 min in the presence of 5 mg NaBH4, while 100 mL of 50 ppm MO, 20 ppm MB, and 50 ppm RhB solutions were reduced entirely within 10 min, 6 min, and 8 min, respectively. The activity of the used catalyst, which was recovered and dried, was tested again for the sixth time and was still up to 95.3%. SbMoSO also performed good stability and durability for reducing organic pollutants and heavy metal ions. The fact of heterovalent conversion of Mo4+ ↔ Mo6+ is conducive to electron transfer and lowers the electron-hole recombination efficiency. Likewise, the stack nanosheet-like morphology of the catalyst can also provide a larger specific surface area and more active sites to facilitate the reduction reaction. Therefore, this study illustrates that the S incorporation into metallic/bimetallic oxides is a promising approach for designing the tuned electronic structure of metallic/bimetallic sulfur-oxide catalysts with boosted catalytic performance.

A New Combination Method of N-doped TiO2 Nanoparticles Synthesis for Heavy Metal Ions Cr(VI) Photoreduction Applications

Through a combination of biosynthetic and hydrothermal methods, N-doped TiO2 photocatalyst has been successfully synthesized using various concentrations of ammonia as a nitrogen source, namely 10% w/w (NTO10), 20% w/w (NTO20), 35% w/w (NTO35), and 50% w/w (NTO50). The synthesis of TiO2 was conducted using Aloe vera (L) Burm F. rind extract as a natural capping agent via the biosynthetic method, followed by a nitrogen doping process via the hydrothermal method. The X-ray Diffraction (XRD) analysis revealed that all phases were anatase. According to the results of the UV-Vis Diffuse Reflectance Spectroscopy (UV-Vis DRS) analysis using the Tauc-Plot method, all N-doped TiO2 samples showed a decrease in the energy gap compared to the TO sample. This indicates that the doping of TiO2 using nitrogen has been successfully doped into TiO2. The photocatalytic activity of N-doped TiO2 was evaluated for the photoreduction of the Cr(VI) model pollutant using a 24-watt LED lamp as a visible light source for 120 minutes. The results indicate that the NTO35 is the best-prepared N-doped TiO2, which showed a reduced rate for the Cr (VI) model pollutant of 50.88%, or two times greater than that of undoped TiO2.

Eu3+-anchoring Zirconium-organic framework for enhancing fluorescence sensing detection sensitivity towards Cr(VI) ions

Heavy metal ion Cr(VI) content has been regarded as one of the most important indicators for discharged industrial wastewater. However, effective identification and detection of Cr(VI) analytes with high sensitivity and selectivity from various water environments remains a significant challenge. In this study, a novel luminescent material (labelled as Eu@Zr-MOF) with high water stability was assembled by post-modification of a zirconium-organic framework with lanthanide Eu3+ ions. And the coordination bonds binding between Eu3+ ions and carboxyl O atoms of Zr-MOF were confirmed by XPS technique. After Eu3+ ions were successfully immobilized within the Zr-MOF lattice, Eu@Zr-MOF exhibits a bright red fluorescence signal which was inherited from the unique luminescent feature of embedded Eu3+ ions. Notably, Eu@Zr-MOF can be deployed as a reliable photochemical sensor for quantitative fluorescence quenching detection of Cr2O72− ions based on the emission peak at 618 nm, showing rather high sensitivity (KSV = 6.746 × 104 M−1) and ultra low detection limit (DL = 5.71 ppb) which has been enhanced more than 3 times compared with pristine Zr-MOF. This study provides a reliable reference for the preparation of novel luminescent MOFs platform for efficient recognition and detection of Cr(VI) analytes.

MIL-125(Ti)-derived double vacancy-induced enhanced visible-light-driven TiO2 p-n homojunction for photocatalytic elimination of OFL and Cr(VI)

The efficient removal of quinolone antibiotics and heavy metal ions Cr(VI) using photocatalysis has attracted increasing attention in the field of environmental remediation. Here, we create a porous TiO2 p-n junction featuring titanium vacancies and oxygen vacancies. The double-deficient TiO2 p-n junction has the same catalytic ability as P25 under UV light. Still, it also can produce copious radicals under visible light excitation to achieve oxidative degradation of ofloxacin and reduced Cr (VI). This is helped by the two reaction centers generated by oxygen and titanium vacancies, the effective light-trapping capacity, and the close interfacial contacts. By adjusting the calcination temperature, oxygen vacancy, and titanium vacancy concentrations, TiO2 p-n junctions with the best photocatalytic activity were produced. In the pH range of 3.63–9.65, TiO2 p-n junctions maintained outstanding activity. The degradation pathway of ofloxacin was examined using theoretical calculations and LC-MS. This study provides a technically guided experimental basis for preparing photocatalytic materials with double-defective p-n junctions.

The effect of cetyltrimethylammonium bromide (CTAB) addition on green synthesis of porous N-doped TiO2 for photoreduction of heavy metal ion Cr(vi).

In this study, porous TiO2 photocatalysts modified by nitrogen (NCT) were successfully synthesized using a combination of green synthesis methods by utilizing Aloe vera (L.) Burm. f. peel and hydrothermal method. In addition, TiO2 was modified by increasing the active surface area using Cetyltrimethylammonium Bromide (CTAB). The X-ray Diffraction (XRD) results indicated that the anatase phase was formed. The result of the Diffuse Reflectance Spectroscopy UV-Vis (DRS UV-Vis) using the Tauc-plot method showed that all porous N-doped TiO2 samples experienced a decrease in the energy gap. This indicates the successful modification of TiO2 by nitrogen, as confirmed by the Fourier Transform Infra-Red (FTIR) result. Field Emission Scanning Electron Microscopy (FESEM) result showed that the synthesized TiO2 had a spherical morphology of 10-30 nm diameter. The Braunauer, Emmett, and Teller (BET) result indicated that the type IV isotherm curve with a mesoporous structure was formed. The NCT0.75 sample had a surface area and pore size of 95.02 m2 g-1 and 8.021 nm, respectively, while the NTi0.75 sample had a surface area and pore size of 90.97 m2 g-1 and 5.161 nm, respectively. The photocatalytic activity of the porous N-doped TiO2 was tested on photoreduction of metal pollutant model Cr(vi). The result demonstrated that the NCT0.75 sample had the most optimal photocatalytic activity by reducing 89.42% of Cr(vi) metal ions.

Simultaneous Determination of Mixed Heavy Metal Ions Cr (III) and Co (II) in Wastewater by Cloud Point Extraction Dual Wavelength Spectrophotometry

Using cloud point extraction technology and the principle of absorbance addition in multi-component system, the mixed metal ions Cr (III) and Co (II) in industrial wastewater were enriched and determined at pH 5.0 and 50℃, using ammonium pyrrolidine dithiocarbamate (APDC) as complexing agent and Triton X-114 as extractant. The results indicate that the contents of Cr (III) and Co (II) can be calculated using a simultaneous equation system. The detection limits for Cr (III) and Co (II) are 0.74 ng/ml and 2.12 ng/ml, respectively. The recovery rates are 95.3% -104.0% and 96.9% -103.5%, respectively. This method has the characteristics of high accuracy, good repeatability, and fast detection speed, and has good practical value.

Simultaneous photocatalytic removal of heavy metal and organic dye over nitrogen and sulfur co-doped hierarchical ZnSnO3/Zn2SnO4 hollow octahedrons

A series of hierarchical N, S co-doped ZnSnO3/Zn2SnO4 porous hollow octahedrons (NS/ZnSnO3/Zn2SnO4) were constructed using the strategy of combining acid-etching technique with in-situ decoration method for the removal of various pollutants in aqueous environment. The optimized NS/ZnSnO3/Zn2SnO4 exhibited an enhanced photocatalytic activity under simulated sunlight, removing heavy metal ion Cr(VI) in 140 min and rhodamine B (RhB) in 50 min, outperforming hollow Zn2SnO4 and ZnSnO3/Zn2SnO4 octahedrons. This raise could be attributed to the synergetic effect of ZnSnO3/Zn2SnO4 heterojunctions, the introduction of N, S elements and unique hierarchical porous hollow morphology. In addition, the photocatalytic activities of NS/ZnSnO3/Zn2SnO4 for removing Cr(VI) and RhB from mixed pollutant solutions were 1.94 and 1.53-folds as high as those of single system, and it also displayed good reusability and stability in co-existing system, suggesting its potential practical applications in the simultaneous removal of various pollutants from contaminated water.

Low-Cost Yet High-Performance Hydrochar Derived from Hydrothermal Carbonization of Duku Peel (<i>Lansium domesticum</i>) for Cr(VI) Removal from Aqueous Solution

Carbon-based adsorbent as a hydrochar (Hc) material with Duku (Lansium domesticum) peel precursors has been successfully synthesized as evidenced by XRD, FT-IR, BET, and SEM analysis. XRD analysis showed the presence of diffraction peaks around 16° and 22° which indicated the presence of carbonaceous material. This is confirmed by FTIR analysis which shows the presence of vibration at 2931 cm−1 of cellulose. SEM data results showed that heterogeneous and has an irregular shape and surface area increased twice from Duku peel to Hc. Duku peel and Hc adsorbent materials were applied to adsorb heavy metal ions Cr(VI). Kinetic parameters of Cr(VI) using Duku peel and Hc showed that the optimum time reached was at 120 min. The adsorption kinetics model of Cr(VI) using Hc tends to follow the PFO model and Langmuir isotherm adsorption. Duku peel material used to adsorb Cr(VI) reached an adsorption capacity of 42.19 mg/g, while in Hc material there was an increase that reached 80.64 mg/g. The thermodynamic parameters of both materials show that the adsorption process is spontaneous.

Bifunctional Sensors Based on Phosphomolybdates for Detection of Inorganic Hexavalent Chromium and Organic Tetracycline.

Exploring effective sensors for detecting possible hazards in a water system are greatly significant. This work proposed a strategy for stable and effective bifunctional sensors via incorporating hourglass-type phosphomolybdates into metal-organic fragments to construct a high-dimensional framework. Two hourglass-type phosphomolybdate-based electrochemical sensors toward heavy metal ion Cr(VI) and tetracycline (TC) detection were designed with the formula [CoII2(H2O)4NaI2][CoII(Hbpe)][NaI(bpe)1.5]{CoII[PV4MoV6O31H6]2}·9H2O (1) and [CoII(H2O)4NaI3][CoII(Hbpe)][CoII(bpe)]{CoII[PV4MoV6O31H6]2}·9H2O (2) [bpe = 1,2-di(4-pyridyl)ethylene]. Structural analysis showed that hybrids 1 and 2 possess three-dimensional POM-supported network features with favorable stability and exhibit reversible redox properties. Experiments found that this kind of hybrids as efficient sensors have excellent electrochemical performance toward Cr(VI) detection with high sensitivities of 0.111 μA·μM-1 for 1 and 0.141 μA·μM-1 for 2, fast response time of 1 s, and low detection limits of 30 nM for 1 and 27 nM for 2, which far meet the standard of WHO for drinking water. Moreover, hybrids 1-2 also exhibit fast responses to TC detection with sensitivities of 0.0073 and 0.022 μA·mM-1 and detection limits of 0.426 and 0.084 mM. This work offers a novel strategy for the purposeful design of efficient POM-based electrochemical sensors for accurate determination of contaminants in a practical water system.

Internal coordination of vanadium industrial waste—Preparation of hydroxyapatite and fluorine wastewater purification

In the vanadium industry, raffinate poses potential environmental risks due to the presence of corrosive fluoride and toxic heavy metals, and waste neutralizing slag (NS) was largely stockpiled given the low economic value, resulting in extensive land occupation and secondary pollution risks. Hydroxyapatite (HAP) was synthesized uniformly from the NS using the hydrothermal method, with no surfactants or additives used except for the three inexpensive reactants required. It was discovered that the pH of the raw material, the temperature, and the length of the hydrothermal reaction all had a significant effect on the adsorption characteristics of the produced HAP. When the conditions for synthesizing HAP were set with a pH of 11.5, a hydrothermal reaction temperature of 120 °C, and a reaction time of 1.5 h, the HAP had the optimum impact on raffinate treatment. The products' characterization by XRD, FTIR, SEM-EDS, and BET corroborated the successful synthesis of homogeneous HAP under the process conditions. The waste stream from the hydrothermal synthesis of HAP was recovered and crystallized to obtain a sodium sulfate by-product which was determined for purity. Adsorbed at room temperature for 1 h, the HAP synthesized by NS has a maximum percentage adsorption of 99.66 % and a saturation adsorption capacity of 43.64 mg/L for F ions in the raffinate. Additionally, the HAP removed over 95 % of the trace heavy metal ions Cr, As, and Cd from the raffinate. The saturated HAP was treated using a hydrothermal regeneration process, and the regenerated HAP retained a fluoride percentage adsorption still reaching 99.28 %. The thermodynamic and leaching experiments reveal that the desorption solution for the regeneration of HAP has the performance to increase the efficiency of vanadium recovery. This technique recycles waste NS to produce high-value HAP, which purification treatment of the raffinate with a high fluorine and contaminants content, solves the problem of treating two types waste of vanadium industry waste (NS and raffinate), and allows for the recycling of valuable element fluorine in vanadium industrial effluent.

Rich Indium-Vacancies In2 S3 with Atomic p-n Homojunction for Boosting Photocatalytic Multifunctional Properties.

Design and development of highly efficient photocatalytic materials are key to employ photocatalytic technology as a sound solution to energy and environment related challenges. This work aims to significantly boost photocatalytic activity through rich indium vacancies (VIn ) In2 S3 with atomic p-n homojunction through a one-pot preparation strategy. Positron annihilation spectroscopy and electron paramagnetic resonance reveal existence of VIn in the prepared photocatalysts. Mott-Schottky plots and surface photovoltage spectra prove rich VIn In2 S3 can form atomic p-n homojunction. It is validated that p-n homojunction can effectively separate carriers combined with photoelectrochemical tests. VIn decreases carrier transport activation energy (CTAE) from 0.64eV of VIn -poor In2 S3 to 0.44eV of VIn -rich In2 S3 . The special structure endows defective In2 S3 with multifunctional photocatalysis properties, i.e., hydrogen production (872.7µmol g-1 h-1 ), degradation of methyl orange (20min, 97%), and reduction in heavy metal ions Cr(VI) (30min, 98%) under simulated sunlight, which outperforms a variety of existing In2 S3 composite catalysts. Therefore, such a compositional strategy and mechanistic study are expected to offer new insights for designing highly efficient photocatalysts through defect engineering.

Fast and efficient removal of dyes and Cr(VI) ion from wastewater using halloysite nanotubes-covalently coated polyurethane sponges

Inspired by the mussel adhesion protein, dopamine was used to prepare polydopamine (PDA)-coated polyurethane sponge (PDA-PUS) via self-polymerization reaction. Halloysite nanotubes (HNTs) were grafted with γ-aminopropyltriethoxysilane (APTES). The new organic-inorganic hybrid adsorption material (HNTs@PUS) was fabricated by covalent link of APTES-grafted HNTs and PDA-PUS through Schiff base reaction/Michael addition. The as-prepared HNTs@PUS showed much higher mechanical stability and compressive property than polyurethane sponge (PUS). HNTs@PUS had 7.7, 7.1, 1.7 and 8.5 times adsorption capacity of PUS for Congo red (CR), Methyl orange (MO), Rhodamine 6 G (R6G) and heavy metal ion Cr(VI), respectively. HNTs@PUS had a fast adsorption rate and most of CR, MO, R6G and Cr(VI) were adsorbed by HNTs@PUS within 20 min. In addition, HNTs@PUS maintained 70.3%, 66.5%, 67.3% and 77.4% of its adsorption capacity for CR, MO, R6G and Cr(VI), respectively, after 5 cycles of regeneration. HNTs@PUS could be easily recovered to avoid secondary contamination. Besides, using HNTs@PUS as adsorbents, a continuous flow adsorption device was developed, through which anionic and cationic dyes and heavy metal ion could be continuously and effectively removed from the flowing solution. These results demonstrated that HNTs@PUS had potentially ideal attributes for use as adsorbents in the ultrafast, high efficiency and large-scale removal of anionic and cationic dyes and heavy metal ions from wastewaters. The fabrication strategy not only solved the problem of the poor recyclability and low permeability of HNTs, but also greatly improved the adsorption capacity of PUS, which might accelerate the application of natural “green” HNTs in wastewater treatment.

In Situ Decoration of ZnSnO3 Nanosheets on the Surface of Hollow Zn2SnO4 Octahedrons for Enhanced Solar Energy Application.

Hierarchical ZnSnO3/Zn2SnO4 porous hollow octahedrons were constructed using the method of combining the acid etching process with the in situ decoration technique for photovoltaic and photocatalytic applications. The composite was used as photoanode of the dye-sensitized solar cells (DSSCs), an overall 4.31% photovoltaic conversion efficiency was obtained, nearly a 73.1% improvement over the DSSCs that used Zn2SnO4 solid octahedrons. The composite was also determined to be a high-performance photocatalyst for the removal of heavy metal ion Cr (VI) and antibiotic ciprofloxacin (CIP) in single and co-existing systems under simulated sunlight irradiation. It was remarkable that the composite displayed good reusability and stability in a co-existing system, and the simultaneous removal performance could be restored by a simple acid treatment. These improvements of solar energy utilization were ascribed to the synergetic effect of the hierarchical porous hollow morphology, the introduction of ZnSnO3 nanosheets, and the heterojunction formed between ZnSnO3 and Zn2SnO4, which could improve light harvesting capacity, expedite electron transport and charge-separation efficiencies.

COF TzDa/Ag/AgBr Z-scheme heterojunction photocatalyst for efficient visible light driven elimination of antibiotics tetracycline and heavy metal ion Cr(VI)

Exploring efficient photocatalysts for eliminating coexisting organic pollutants and heavy metal ions is important for sustainable and green environmental purification. Herein, in-situ precipitation-deposition of AgBr onto COF TzDa feasibly fabricated a new heterojunction composite COF TzDa/AgBr, which readily transformed to COF TzDa/Ag/AgBr under exposure to light. The structure, morphology, composition, optical and electrochemical properties of this composite were characterized through various techniques. The activities of COF TzDa/Ag/AgBr in degrading antibiotics tetracycline (TC) and reducing Cr(VI) under simulated visible-light were extensively improved compared with bare COF TzDa, AgBr and their physical mixture. Credited to the synergism among TC, Cr(VI) and the photocatalyst, COF TzDa/Ag/AgBr demonstrated even higher efficiency in simultaneously removing TC/Cr(VI) mixture than for the single pollutant. Furthermore, plausible TC degradation intermediates and pathways were postulated by HPLC-MS analysis. Investigations on band structure, radicals quenching and ESR spectra concluded a Z-scheme charge transfer mechanism with Ag NPs as electron mediator in COF TzDa/Ag/AgBr, which revealed that O2− and h+ were responsible for degrading TC, while photo-generated electrons reduced toxic Cr(VI) to non-toxic Cr(III). The enhanced performance of COF TzDa/Ag/AgBr should stem from the reinforced visible-light adsorption, increased surface areas, accelerated charge transfer and separation, and inhibited Ag/AgBr aggregation. COF TzDa/Ag/AgBr also displayed good stability during the recycled treatment of TC and Cr(VI), while TC degradation under COF TzDa/Ag/AgBr was not obviously influenced by common environmental factors. Thus, this work might offer a promising strategy for the treatment and purification of wastewater containing organic pollutants and heavy metal ions.

Three Anderson-type POMOFs with bis(pyrimidine)-bis(amide) ligands: Synthesis, fascinating structures and performances of electrochemical sensing and dye adsorption

Three new Anderson-type polyoxometalate (POM)-based metal–organic frameworks (POMOFs) [Co3(L1)(TeMo6O24)(H2O)10]·8H2O (1), [Co3(L2)(TeMo6O24)(H2O)10]·8H2O (2) and [Cu3(L1)(TeMo6O24)(H2O)10]·6H2O (3) (L1 ​= ​N,N′-bis(4-pyrimidinecarboxamido)-1,2-ethane, L2 ​= ​N,N′-bis(4-pyrimidinecarboxamido)-1,4-butane) were obtained under 90 ​°C aqueous solution for two days. POMOFs 1–3 show fascinating 3D framework structures formed by transition metal linking bis(pyrimidine)-bis(amide) ligands and Anderson-type [TeMo6O24]6– anions. The carbon paste electrodes bulk-modified by POMOFs 1–3 (1-, 2-, 3-CPEs) have good bifunctional electrocatalytic performance towards the oxidation of ascorbic acid and the reduction of potassium bromate, potassium nitrite and heavy metal ions Cr(VI). 1-, 2-, 3-CPEs can be used as electrochemical sensors for the detection of Cr(VI), the limits of detection (LODs) are 0.389 ∼ 0.422 ​μM, which are lower than the 1.0 ​μM standard set by the WHO. In addition, the adsorption properties of POMOFs 1–3 on organic dyes gentian violet (GV) and methyl orange (MO) were investigated.