Distinguished Cr(VI) capture with rapid and superior capability using polydopamine microsphere: Behavior and mechanism

Facile preparation of hierarchical porous polydopamine microspheres for rapid removal of chromate from the wastewater

Abstract

Cr(VI) containing industrial wastewaters are highly toxic and carcinogenic, and severely threats living creatures and the environment. Therefore, it is highly desired yet challenging to develop an available and economical adsorbent for simultaneously detoxifying Cr(VI) anions to Cr(III) ions and removing them from the wastewater. Here we propose a facile method for rapid removal of Cr(VI) ions from the wastewater by using a synthetic polydopamine microsphere (PPM) adsorbent with hierarchical porosity. The as-prepared PPM exhibits high Cr(VI) removal capacity of 307.7 mg/g and an outstanding removal efficiency. They can effectively decrease the Cr(VI) concentration to lower than 0.05 mg/L well below the limits for drinking water standard of WHO regulations in 60 s at pH 2. More importantly, PPMs can reduce the lethal Cr(VI) anions to Cr(III) ions with low toxicity, and simultaneously immobilize them on the matrices of PPMs.

Graphical abstract

New Mussel Inspired Polydopamine-Like Silica-Based Material for Dye Adsorption

A straightforward and economic procedure has been developed for the synthesis of a new polydopamine-like silica-based material that has been obtained by oxidation of catechol with KIO4 followed by reaction with 3-aminopropyltrimethoxysilane. All techniques adopted for characterization showed that the obtained material is rich in different functional groups and the morphological analyses revealed dimensions in the nanometric range. The hybrid material has been characterized by several techniques showing its polydopamine-like nature, and preliminary observations for dye adsorption have been reported.

Three dimensional flower-like magnetic polyethyleneimine@MoS2 composites for highly efficient removal of Cr(VI) and Pb(II) ions

Magnetic Fe₃O₄ nanoparticles were coated by polyethyleneimine (PEI), and then Fe₃O₄@PEI was further modified with MoS₂ by the hydrothermal method to fabricate 3D flower-like structured magnetic polyethyleneimine@MoS₂ (MP@MoS₂) composites, and the composites were served as efficient adsorbents to capture Cr(VI) and Pb(II) from aqueous solution. The effects of temperature, pH, shaking time and environmental conditions on adsorption performance of MP@MoS₂ towards Cr(VI) and Pb(II) have been conducted by batch adsorption experiments. The prepared MP@MoS₂ exhibited high adsorption capacities (192.30 mg/g for Cr(VI) at pH 3.0 and 256.41 mg/g for Pb(II) at pH 6.0) and the adsorption equilibrium could be achieved in a short time. Moreover, MP@MoS₂ composites with high saturation magnetization could be simply separated under an external magnet. Combined experiments and spectral analysis, the underlying adsorption mechanism for Cr(VI) on MP@MoS₂ was mainly attributed to the reduction of Cr(VI) to Cr(III), and the removal of Pb(II) was due to the complexation with sulfur groups and amino-groups. Consequently, the prepared 3D flower-like structured MP@MoS₂ has a great potential for the practical application in removing Cr(VI) and Pb(II) from the aquatic environment.

Poly(acryloyl hydrazide)-grafted cellulose nanocrystal adsorbents with an excellent Cr(VI) adsorption capacity

In this study, we prepared poly(acryloyl hydrazide) (PAH)-grafted cellulose nanocrystal (CNC-PAH) particles via the atom transfer radical polymerization method for application to Cr(VI) adsorption. The closely-packed PAH chains grafted on the cellulose nanocrystal (CNC) surface provide a high density of amine groups that can adsorb Cr(VI) through strong electrostatic, hydrogen bonding and chelating interactions. CNC-PAH exhibited the optimum Cr(VI) adsorption capacity at the solution pH = 3, where its electrostatic attraction with Cr(VI) was maximized. Cr(VI) was chemisorbed in CNC-PAH by following the Langmuir isotherm mechanism (homogeneous monolayer adsorption). The Cr(VI) adsorption kinetics of CNC-PAH was controlled predominantly by intra-particle diffusion resistance imparted by the PAH shell layer. Thermodynamic analysis revealed that Cr(VI) adsorption of CNC-PAH is a spontaneous and endothermic process. Importantly, CNC-PAH grafted with the higher M_w (∼50 kg mol^-1) PAH exhibited a rapid Cr(VI) adsorption rate and remarkably high Cr(VI) adsorption capacity (∼457.6 mg g^-1 at 298.15 K), exceeding those of previously reported adsorbents owing to its numerous Cr(VI)-adsorptive amine groups provided by the closely-packed grafted PAH polymers. Furthermore, CNC-PAH showed excellent reusability to maintain its high adsorption ability during repeated adsorption-desorption cycles owing to the covalently binding nature of the PAH polymers.

Polydopamine modified cyclodextrin polymer as efficient adsorbent for removing cationic dyes and Cu2

An eco-friendly polydopamine composite adsorbent (CD-CA/PDA) based on cyclodextrin polymer was prepared for cationic dyes and metals removing. CD-CA/PDA, combining the advantages of cyclodextrin and polydopamine, which has quite abundant carboxyl and catechol groups, so methylene blue (MB), malachite green (MG), crystal violet (CV) and copper ion (Cu²⁺) can be easily removed by electrostatic force. Adsorption kinetic results showed all adsorption process fitted well with pseudo-second-order model. In addition, the isotherm fitted results showed that the adsorption processes of CD-CA/PDA on MG and Cu²⁺ were consistent with sips model, while the adsorption processes of MB and CV agreed well with Freundlich and Langmuir model, respectively. The fitted adsorption capacities of CD-CA/PDA for MB, MG, CV and Cu²⁺ were 582.95 mg/g (1.82 mmol/g), 1174.67 mg/g (3.22 mmol/g), 473.01 mg/g (1.16 mmol/g) and 73.64 mg/g (1.16 mmol/g), respectively. Moreover, it is worth noting that cationic dyes have no competitive adsorption in series. CD-CA/PDA is of great recyclability, and can be reused by at least 5 times. Due to the facile and eco-friendly preparation process and excellent adsorption performance, CD-CA/PDA has a great potential in the field of wastewater treatment.

Greywater and bacteria removal with synchronized energy production in photocatalytic fuel cell based on anodic TiO2/ZnO/Zn and cathodic CuO/Cu

An approach that can recuperate of energy from wastewater treatment process is highly necessitate and would help to surmount the both environmental pollution and energy crisis issues. A photocatalytic fuel cell (PFC) employing an anodic TiO₂/ZnO/Zn and a cathodic CuO/Cu has been applied to degrade the raw greywater, which realized advanced organics destruction, bacteria disinfection, and synchronously electricity production. The improved photocatalytic performance has been observed when the cell was incorporated with anodic TiO₂/ZnO/Zn under UV and sunlight irradiation due to the enhanced electric field conductivity of the catalysts and heterojunction interface of TiO₂. In the constructed UV-activated PFC system, the electricity production capability was observed with the measured voltage and power density of 868 mV and 0.0172 mW cm^-2, respectively. Advanced chemical oxygen demand (COD) removal efficiency of greywater achieved a 100% completion within 60 min of light irradiation. The Escherichia coli (E. coli) colonies decreased significantly and accounted ∼99% disinfection efficiency. Moreover, the photoelectrochemical and photoluminescence (PL) experiments elucidated that the charge carrier separation efficiency were higher when TiO₂ was coupled to ZnO. The organic matter elimination principle was assessed by radical trapping experiment, and the findings indicated that the hydroxyl (OH) radical and hole (h⁺) appeared as major functions in the reaction. The stable cycle operation of the cell has been also obtained owing to the stable and film-type materials of anodic material. This performance was among the highest documented for PFC using real wastewater effluent as the fuel source.

Highly Efficient Removal of Methylene Blue Dye from an Aqueous Solution Using Cellulose Acetate Nanofibrous Membranes Modified by Polydopamine

A new type of deacetylated cellulose acetate (DA)@polydopamine (PDA) composite nanofiber membrane was fabricated by electrospinning and surface modification. The membrane was applied as a highly efficient adsorbent for removing methylene blue (MB) from an aqueous solution. The morphology, surface chemistry, surface wettability, and effects of operating conditions on MB adsorption ability, as well as the equilibrium, kinetics, thermodynamics, and mechanism of adsorption, were systematically studied. The results demonstrated that a uniform PDA coating layer was successfully developed on the surface of DA nanofibers. The adsorption capacity of the DA@PDA nanofiber membrane reached up to 88.2 mg/g at a temperature of 25 °C and a pH of 6.5 after adsorption for 30 h, which is about 8.6 times higher than that of DA nanofibers. The experimental results showed that the adsorption behavior of DA@PDA composite nanofibers followed the Weber's intraparticle diffusion model, pseudo-second-order model, and Langmuir isothermal model. A thermodynamic analysis indicated that endothermic, spontaneous, and physisorption processes occurred. Based on the experimental results, the adsorption mechanism of DA@PDA composite nanofibers was also demonstrated.

Fabrication of core@shell structural Fe-Fe2O3@PHCP nanochains with high saturation magnetization and abundant amino groups for hexavalent chromium adsorption and reduction

The rational design of novel adsorption materials is imperative to remove toxic metal species from the polluted water. Herein, a core@shell structural Fe-Fe₂O₃@poly (hexachlorocyclotriphosphazene-co-polyethylenimine) (Fe-Fe₂O₃@PHCP) magnetic nanochain with high saturation magnetization was fabricated and used for effective adsorption and reduction of hexavalent chromium. The morphology and microstructure of Fe-Fe₂O₃@PHCP were characterized by scanning electron microscopy, transmission electron microscopy, Fourier transform infrared spectroscopy, X-ray diffraction and X-ray photoelectron spectroscopy. The effects of concentration, pH, contact time, temperature and coexisting ions on Cr (VI) removal were studied. Four kinetic models (pseudo-first-order, pseudo-second-order, Bangham and intraparticle diffusion models) and two isotherm models (Freundlich and Langmuir) were used to fit experimental data. Results show the adsorption capacity of Fe-Fe₂O₃@PHCP for Cr (VI) is up to 229.0 mg g^-1. The excellent performance was ascribed to the favorable reduction of Cr (VI) to Cr (III), followed by the chelation of Cr (III) with imino groups. Meanwhile, the residual Cr (VI) were adsorbed on protonated amino and imino groups. The adsorption process is exothermic and spontaneous and nicely follows pseudo-second-order kinetics, intraparticle diffusion model and Langmuir isotherm model. These results indicated that easily separable Fe-Fe₂O₃@PHCP magnetic nanochains could be a promising adsorbent to remediate chromate wastewater.

In situ construction efficient visible-light-driven three-dimensional Polypyrrole/Zn3In2S6 nanoflower to systematically explore the photoreduction of Cr(VI): Performance, factors and mechanism

Photoreduction of highly toxic Cr(VI) has been regarded as an efficient and green method to achieve water purification. In this process, better charge carrier separation is vital to achieving excellent performance. Besides, it is vital to systematically explore the influencing factors and reaction mechanism. Herein, a novel 3D PPy/Zn₃In₂S₆ nanoflower composite was successfully fabricated via in-situ polymerization. The remarkable conductivity of PPy provides a good electron transport path to facilitate the separation and migration of charge carriers, which benefits to the activity improvement. The results show that 5% PPy/Zn₃In₂S₆ exhibits superior photocatalytic activity with almost 100% Cr(VI) reduction just within 24 min and 99.4% of Methyl orange (MO) is degraded in 25 min. On this basis, factors of different catalyst dosage, concentration, ions and pH under the reduction system were systematically investigated. Especially, different organic acids were in-depth analyzed and the activity could be significantly enhanced just adding 0.1 mmol organic acids. 5% 3D PPy/Zn₃In₂S₆ nanoflower composites (with tartaric acid) exhibits superior photocatalytic activity, which can achieve 100% photoreduction of Cr(VI) just within 6 min. Finally, a possible reaction mechanism was proposed. Moreover, 3D PPy/Zn₃In₂S₆ nanoflower also presented an efficient photodegradation activity for organic pollution.

Nature-mimic fabricated polydopamine/MIL-53(Fe): efficient visible-light responsive photocatalysts for the selective oxidation of alcohols

PDA/MIL-53(Fe) nanocomposites prepared via a nature-mimicking method were efficient catalysts towards the photocatalytic selective oxidation of alcohols to aldehydes or ketones by a direct holeoxidation process under visible-light illuminated conditions.

Highly efficient removal of Cr(vi) ions from wastewater by the pomegranate-like magnetic hybrid nano-adsorbent of polydopamine and Fe3O4 nanoparticles

Fe₃O₄ nanoparticles have attracted extensive attention for solving Cr(vi) pollution because they can effectively reduce Cr(vi) to the less toxic and less soluble Cr(iii)-containing species.

Efficient Degradation of Norfloxacin and Simultaneous Electricity Generation in a Persulfate-Photocatalytic Fuel Cell System

Photocatalytic fuel cell (PFC) has been verified to be a promising technique to treat organic matter and recover energy synchronously. Sulfate radicals (SO4·−), as a strong oxidant, have obvious advantages in the degradation of refractory pollutants compared with hydroxyl radicals (·OH), which is the dominant radical in PFC. This study reports a coupling method of PFC and persulfate (PS) activation to promote the degradation of antibiotic norfloxacin (NOR) and simultaneous electricity generation. The added PS as an electron acceptor could be activated by photoelectric effects to produce SO4·− at the electrodes-electrolyte interface. In the solution, PS as supporting electrolyte could accelerate the electron transfer and also be activated by ultraviolet (UV) light irradiation, which could extend the radical oxidation reaction to the whole solution and improve the PFC performance. The performance comparison among different systems indicated the excellent synergistic effect of PFC and PS activation for improving NOR degradation and electricity generation. The effects of influencing factors including initial pH, PS concentration, and initial NOR concentration on the degradation of NOR were investigated extensively to find out the optimal conditions. Moreover, according to the results of radical capture experiments, the significantly contribution of both SO4·− and ·OH to the degradation of NOR was demonstrated and a tentative function mechanism for the NOR degradation in the proposed system was provided. Finally, total organic carbon and real wastewater treatment confirmed the high mineralization and practical applicability of the proposed PFC/PS system.

Fate of environmental pollutants

This annual review covers the literature published in 2018 on topics related to the occurrence and fate of environmental pollutants in wastewater. Due to the vast amount of literature published on this topic, we have discussed only a portion of the quality research publications, due to the limitation of space. The abstract search was carried out using Web of Science, and the abstracts were selected based on their relevance. In a few cases, full-text articles were referred to understand new findings better. This review is divided into the following sections: antibiotic-resistant bacteria (ARBs) and antibiotic-resistant genes (ARGs), disinfection by-products (DBPs), drugs of abuse (DoAs), estrogens, heavy metals, microplastics, per- and polyfluoroalkyl compounds (PFAS), pesticides, and pharmaceuticals and personal care products (PPCPs), with the addition of two new classes of pollutants to previous years (DoAs and PFAS).

A Facile and Simple Method for Preparation of Novel High-Efficient Form-Stable Phase Change Materials Using Biomimetic-Synthetic Polydopamine Microspheres as a Matrix for Thermal Energy Storage

Polydopamine microspheres (PDAMs), synthesized using a biomimetic method, were used as a matrix for polyethylene glycol (PEG) to develop a novel high-efficient form-stable phase change material (PEG/PDAM) using a simple vacuum impregnation strategy. The PDAMs were first used as a support for the organic phase change materials, and the biomimetic synthesis of the PDAMs had the advantages of easy operation, mild conditions, and environmental friendliness. The characteristics and thermal properties of the PEG/PDAMs were investigated using SEM, FTIR, XRD, TGA, DSC, and XPS, and the results demonstrated that the PEG/PDAMs possessed favourable heat storage capacity, excellent thermal stability, and reliability, and the melting and freezing latent heats of PEG/PDAM-3 reached 133.20 ± 2.50 J/g and 107.55 ± 4.45 J/g, respectively. Therefore, the PEG/PDAMs possess great potential in real-world applications for thermal energy storage. Additionally, the study on the interaction mechanism between the PEG and PDAMs indicated that PEG was immobilized on the surface of PDAMs through hydrogen bonds between the PEG molecules and the PDAMs. Moreover, the PDAMs can also be used as a matrix for other organic materials for the preparation of form-stable phase change materials.

Removal of the heavy metal ion nickel (II) via an adsorption method using flower globular magnesium hydroxide

To remove toxic Ni(II) ions from wastewater, a novel flower globular magnesium hydroxide (FGMH) was prepared by a gentle method using trisodium citrate as a crystal modifier. This material exhibited a high specific surface area. The synthesized products and adsorption mechanism for Ni(II) ions were examined by diverse characterization technologies and methods. FGMH was employed to remove Ni(II) ions by the adsorption method. The effects of various parameters, viz., the amount of adsorbent, contact time, temperature and pH, on the removal rate by the adsorbent were investigated in detail. The kinetic data fitted well with a pseudo-second-order model and experimental equilibrium adsorption data conformed to a Langmuir isotherm under optimized conditions. The optimal process parameters included 30 mg of FGMH, a 50 min contact time, pH values between 6.07 and 7.71 for the Ni(II) solution, and adsorption at room temperature for 50 mL of 80 mg/L Ni(II) solution. The percentage of removal efficiency was found to be above 92.64%, and the maximum adsorption capacity of MH was 287.11 mg/g under optimum adsorption conditions. The analyses indicated that the Ni(II) ions were chemisorbed on the FGMH surface.

Heterotopic formaldehyde biodegradation through UV/H2 O2 system with biosynthetic H2 O2

Biodegradation was regarded an environmentally benign and cost-effective technology for formaldehyde (CH₂ O) removal. However, the biotoxicity of CH₂ O inhibited microbial activity and decreased removal performance. We developed a novel heterotopic CH₂ O biodegradation process that combined bioelectrochemical system (BES) and UV/H₂ O₂ . Instead of exogenous addition, H₂ O₂ was biosynthesized with electron transferred from electrochemically active bacteria. Heterotopic biodegradation of CH₂ O was more efficient and faster than in situ biodegradation, as confirmed by 69%-308% higher removal efficiency and 98% shorter degradation time. Operated under optimal conditions for 30 min, which are optical distance of 2 cm, initial H₂ O₂ concentration of 102 mg/L, and pH 3, heterotopic biodegradation removed 78%, 73%, 49%, and 30% of CH₂ O with 6, 8, 10, and 20 mg/L initial concentration. Mild formation of hydroxyl radicals from UV/H₂ O₂ is beneficial to sustainable CH₂ O degradation and efficient H₂ O₂ utilization. Heterotopic biodegradation is a promising technology for efficient degradation of other organic compounds with biological toxicity. PRACTITIONER POINTS: H₂ O₂ biosynthesis through electrochemically active bacteria (EAB) served as source of ·OH for CH₂ O removal in UV/H₂ O₂ . Heterotopic CH₂ O biodegradation avoided the biotoxicity of CH₂ O. Heterotopic biodegradation of CH₂ O saved 98% time than in-situ biodegradation. Heterotopic CH₂ O biodegradation improved 69%-308% efficiency than in-situ.

A method for particulate matter 2.5 (PM2.5) biotoxicity assay using luminescent bacterium

The ability to analyze biotoxicity of atmospheric pollution plays an important role in public health. It provides the potential to directly analyze the health information of at-risk individuals. Although air quality standards have received significant attention in many countries, the potential for better biotoxicity assessment has remained largely unexplored. Here we propose a method using one kind of luminescent bacterium Photobacterium phosphereum to detect the biotoxicity of atmospheric particulate matter ≤ 2.5 µm (PM_2.5). Combined with the results of air pollution data of the year 2013-2014, this method has been proven to have good biotoxicity detection performance, and can evaluate the severity of at least 85% of PM_2.5 related biotoxicity in Shanghai during this time period. Based on an established algorithm of this detection system, the biotoxicity of twelve PM_2.5 real samples (collected over a month) were tested and divided into different biotoxicity levels. It allows an effective evaluation of biotoxicity of PM_2.5 due to the quick and sensitive response of bioluminescence to the concentration of toxic components, which provides a valuable reference to evaluate the biotoxicity of PM_2.5. This established method can be easily applied to the analysis and evaluation of any other PM_2.5 samples assay by following the steps.

Enhanced visible light photoreduction of aqueous Cr(VI) by Ag/Bi4O7/g-C3N4 nanosheets ternary metal/non-metal Z-scheme heterojunction

In this paper, we successfully constructed a ternary metal/non-metal nanomaterial which can synergize Z-scheme heterojunction and plasmonic metal/semiconductor for enhancing visible light photoreduction of aqueous Cr(VI). The as-formed ternary metal/non-metal nanomaterial was composed of g-C₃N₄ nanosheets mutual modified by Ag nanoparticles and Bi₄O₇. In the ternary nanomaterial, g-C₃N₄ nanosheets and Bi₄O₇ fabricated Z-scheme heterojunction, g-C₃N₄ nanosheets and Ag nanoparticles formed plasmonic metal/semiconductor system, synchronously. The photodeposition experiments were designed to indirect demonstrate the Z-scheme heterojunction via photocatalytic oxidation and reduction deposition reactions, AgNO₃ was used as the electron acceptor and Pb(NO₃)₂ as the electron donor, photocatalytic reduction product and oxidation product were selectively deposited on g-C₃N₄ nanosheets and Bi₄O₇, respectively, revealing the Z-scheme heterojunction was definite formed. In addition, X-ray photoelectron spectroscopy (XPS), photoluminescence (PL), UV-vis absorption, and Fourier-transform infrared spectroscopy (FTIR) were studied to indicate that the plasmonic metal/semiconductor system was existent in the ternary nanomaterial. The visible light photoreduction of ternary Ag/Bi₄O₇/g-C₃N₄ nanosheets was evaluated by photoreducing aqueous Cr(VI). The photoreduction results show that the ternary Ag/Bi₄O₇/g-C₃N₄ nanosheets is much higher than the pristine bulk g-C₃N₄ and g-C₃N₄ nanosheets.

Degradation of cefradine in alga-containing water environment: a mechanism and kinetic study

Large quantities of antibiotics are manufactured, used, and eventually discharged into alga-containing water environment as prototypes, by-products, or transformation products. Different activities of Chlamydomonas reinhardtii toward cefradine (CFD) were studied, and the results indicated that CFD is resistant (removal rate of 5.45-14.72%) in simulated natural water environment. Cefradine was mainly removed by hydrolysis, adsorption, desorption, photodecarboxylation, and photoisomerization. The effects of C. reinhardtii density, initial solution pH, and different light sources on CFD removal efficiency were investigated. The optimum conditions occurred at a density of algae 10 × 10⁴ cells/mL, a solution pH of 9.0, and the ultraviolet (UV) light. Additionally, the removal kinetics under 16 different conditions was explored. The results showed that the removal of CFD fits well with a pseudo-first-order kinetic, and the half-life times are from 0.8 to 261.6 days. This study summarizes the CFD removal mechanisms in alga-containing water environment, highlights the important role played by light irradiation in eliminating CFD, and obtains the important kinetic data on CFD removal.

Mechanochemically Synthesised Coal-Based Magnetic Carbon Composites for Removing As(V) and Cd(II) from Aqueous Solutions

The continued decrease in water quality requires new advances in the treatment of wastewater, including the preparation of novel, effective, environmentally friendly, and affordable sorbents of toxic pollutants. We introduce a simple non-conventional mechanochemical synthesis of magnetically responsive materials. Magnetic lignite and magnetic char were prepared by high-energy ball co-milling from either raw Slovak lignite or coal-based char together with a ferrofluid. The products were characterised by X-ray diffraction, electron microscopy, ⁵⁷Fe Mössbauer spectroscopy, X-ray photoelectron spectroscopy (XPS), volumetric magnetic susceptibility, and low-temperature nitrogen adsorption, and both magnetic carbons were comparatively tested as potential sorbents of As(V) oxyanions and Cd(II) cations in aqueous solutions. The magnetic char was an excellent sorbent of As(V) oxyanions (Q_m = 19.9 mg/g at pH 3.9), whereas the magnetic lignite was less effective. The different sorption properties towards arsenic anions may have been due to different oxidation states of iron on the surfaces of the two magnetic composites (determined by XPS), although the overall state of iron monitored by Mössbauer spectroscopy was similar for both samples. Both magnetic composites were effective sorbents for removing Cd(II) cations (Q_m (magnetic lignite) = 70.4 mg/g at pH 6.5; Q_m (magnetic char) = 58.8 mg/g at pH 6.8).

The porous structure effects of skeleton builders in sustainable sludge dewatering process

Dewatering from sludge is an important sustainable issue in recent years, in this work, we found the unique behavior: Skeleton builder additions can improve the dewatering performance greatly, which related to the different pore structure of skeleton builder. As compared to the coal ash, sawdust and rice husk char are easier to construct porous channels in the sludge body, which is responsible for the discharge of water. the dewatering efficiency can increased from approximately 30%-65% by pipe network effect and interlayer channel effect, a sufficient amount of skeleton builders establish a complete pipe drainage network in the sludge body, allowing the water to be discharged fluently. Moreover, the skeleton builders can cause the sludge body to form a layered structure. Under the combined action of pipe network effect and interlayer channel effect, the deep-dewatering effect increased largely by the addition of skeleton builders.

Preparation and Characterization of Nanoporous Activated Carbon Derived from Prawn Shell and Its Application for Removal of Heavy Metal Ions

The aim of this study was to optimize the adsorption performance of activated carbon (AC), derived from the shell of Penaeus vannamei prawns, on heavy metal ions. Inexpensive, non-toxic, and renewable prawn shells were subjected to carbonization and, subsequently, KOH-activation to produce nanoporous K-Ac. Carbonized prawn shells (CPS) and nanoporous KOH-activated carbon (K-Ac) from prawn shells were prepared and characterized by FTIR, XRD, BET, SEM, and TEM. The results showed that as-produced K-Ac samples were a porous material with microporous and mesoporous structures and had a high specific surface area of 3160 m²/g, average pore size of about 10 nm, and large pore volume of 2.38 m³/g. Furthermore, batches of K-Ac samples were employed for testing the adsorption behavior of Cd²⁺ in solution. The effects of pH value, initial concentration, and adsorption time on Cd²⁺ were systematically investigated. Kinetics and isotherm model analysis of the adsorption of Cd²⁺ on K-Ac showed that experimental data were not only consistent with the Langmuir adsorption isotherm, but also well-described by the quasi-first-order model. Finally, the adsorption behaviors of as-prepared K-Ac were also tested in a ternary mixture of heavy metal ions Cu²⁺, Cr⁶⁺, and Cd²⁺, and the total adsorption amount of 560 mg/g was obtained.

Phosphorus Competition in Bioinduced Vivianite Recovery from Wastewater

Phosphorus undergoes a one-way flow from minerals to soil to water, which creates a phosphorus crisis as well as aquatic eutrophication. Dissimilatory metal reduction bacterial (DMRB)-induced vivianite recovery from wastewater is a promising route to solve these problems synthetically. In this study, phosphorus competition between biomass growth and bioinduced vivianite mineralization was investigated at the batch scale. Biomass growth leads to phosphorus utilization over vivianite mineralization. Geobacter was selected as the main functional microorganism and presented higher vivianite recovery rates (20-48%) than sewage biomass (7-33%). An optimal Fe/P stoichiometric ratio of 1:1 was observed for both sewage biomass and Geobacter-inoculated batches. The highest vivianite yield of 4.3 mM was obtained in Geobacter-inoculated batches at a Fe:P of 1:1, with values 59% higher than those at a Fe:P of 1:0.67 (equal to the Fe/P molar ratio in vivianite). Sufficient PO₄^3- stimulated cell growth and yielded a higher Fe³⁺ reduction rate and vivianite yield. Nevertheless, excessive PO₄^3- facilitated the precipitation of KFe₃ (PO₄)₂(OH)·8H₂O and Fe₇ (PO₄)₆, which inhibited vivianite synthesis. In the optimal Geobacter batch, the μ -S curve indicated a mixed order reaction (0 < x < 1) for both vivianite formation and biomass growth. The vivianite growth series proceeded as follows: tiny blue particles, plain pieces, dark blue nodules, and large spherical crystals.

Physiological responses of Suaeda glauca and Arabidopsis thaliana in phytoremediation of heavy metals

The over discharge of mine tailing cause consequent heavy metal pollution. Phytoremediation as one of the most viable and efficient method for this problem has aroused much attention. In this research, the growth and physiological responses of Suaeda glauca and Arabidopsis thaliana plants were investigated, and the soil conditions (pH and enzyme activity) were evaluated further under varied levels of cadmium (Cd), lead (Pb) and manganese (Mn). The results showed that heavy metals could inhibit the growth of plants. The fresh weight and photosynthetic pigments contents of Suaeda and Arabidopsis decreased with the increased concentration of Cd, Pb and Mn. As a monitoring plant, growth status of Arabidopsis showed good dose-effect when treated by heavy metals. S. glauca showed better tolerance capacity for Cd, Pb and Mn, when compared with Arabidopsis. Moreover, the physical and chemical properties of soil were significantly improved after phytoremediation. The soil catalase activity decreased with increased concentration of metal treatments, which showed similar regularity with microbial community. Changes of microbial community could not only indicate the soil environment but also suggest that S. glauca plants had better influences on the soil microbial environment. The introduction of plants resulted in a 0.5-0.8 units change in soil pH compared with the initial pH level. The present study provided the potential of S. glauca plants for phytoremediation in contaminated soil. Microbial community of Suaeda and Arabidopsis were evaluated and showed different regularity because of the rhizosphere effect. Soil microorganisms played an important role in the process of bioremediation. Meantime the main problems about physical and chemical properties of mine tailings were improved. It could be of great significance to the large-scale resource utilization and economical remediation of mine tailings.

Study on the interaction mechanism between cefradine and Chlamydomonas reinhardtii in water solutions under dark condition

Our research investigated the hormesis effect of cefradine on the specific growth rates (μ) of single-celled algae (Chlamydomonas reinhardtii) from aqueous solutions. We found the specific growth rate of C. reinhardtii slightly increased with cefradine concentrations within the range 0.5-10 mg/L. Effects of algae density, initial solution pH, and temperature on the adsorption batch assays were investigated. The optimum conditions for cefradine adsorption occurred at a density of 5 × 10⁶ algae cells/mL, a solution pH of 7.0, and a temperature of 25.0 °C. A Box-Behnken design was employed to evaluate correlations between influential factors and cefradine adsorption. The results showed a significant interaction between algae density and temperature. The maximum removal rate could reach 50.13% under the optimal conditions. Additionally, the adsorption mechanisms were explored through Langmuir and Freundlich isotherm equations, adsorption kinetics, and thermodynamics. The results suggested that the adsorption process was monolayer, spontaneous, and endothermic with an increase in randomness at the algae-solution interface, which followed a pseudo-second-order model. All the data indicated that the alga performed a better removal capacity in the antibiotic-containing wastewater treatment process. This study lays the groundwork for a better understanding of the interaction mechanism between cefradine and Chlamydomonas reinhardtii in water solutions under dark condition.

Efficient removal of Pb(II), Cr(VI) and organic dyes by polydopamine modified chitosan aerogels

Chitosan is highly suitable for removing metal ions and dyes from water; however, the sorption performance, stability and recycling are still critical issues in practical applications. Herein, polydopamine-modified-chitosan (CS-PDA) aerogels were synthesized through dopamine self-polymerization and glutaraldehyde cross-linking reactions to enhance the adsorption capacity and acid resistance of chitosan. The self-polymerization of dopamine and gelation of chitosan were accomplished simultaneously, simplifying the synthesis process of CS-PDA aerogels, which is meaningful for the popularization and industrial application of adsorbent. CS-PDA exhibited superior adsorption performances in the removal of Cr(VI), Pb(II) and organic dyes. Adsorption isotherms and kinetic data were well fitted by Langmuir and pseudo-second-order kinetic models. The maximum adsorption capacities of CS-PDA for Cr(VI) and Pb(II) were 374.4 and 441.2 mg g^-1, respectively. After eight cycles, adsorption capacity of CS-PDA showed no obvious decline. These superiorities make CS-PDA a promising multifunctional adsorbent for the purification of metal ions and dyes.

Use of nicotinamide decorated polymeric cryogels as heavy metal sweeper

Cryogels are synthetic polymers used in adsorption experiments in recent years. Because of their macropores, they provide an excellent advantage as an adsorbent in continuous and batch adsorption processes. In this study, nicotinamide (NAA) decorated poly(2-hydroxyethyl methacrylate-glycidyl methacrylate), poly(HEMA-GMA), cryogels were synthesized. Heavy metal adsorption was carried out in wastewater obtained from six different sources in Çorum, Turkey. This study has a novelty regarding the application, i.e., it is the first time to use a polymeric adsorbent for the removal of 15 different heavy metal at the same time without any competition (despite the fact that there is a competition between the metals, the only thing is the removal regarding the purpose the study) as a heavy metal sweeper. Inductively coupled plasma-mass spectrometer (ICP-MS) was used for the determination of the initial amount of heavy metal in the wastewater samples. Adsorption studies were performed using poly(HEMA-GMA) and NAA-decorated poly(HEMA-GMA) cryogel to see the effect of NAA decoration. Higher adsorption capacity was achieved using NAA decorated poly(HEMA-GMA) cryogel. The total heavy metal amount adsorbed from six different sources was about 686 and 387 mg for poly(HEMA-GMA)-NAA and poly(HEMA-GMA) cryogels, respectively. The highest heavy metal adsorption value was obtained in the wastewater from source 2, and Zn (II) was the heavy metal adsorbed most for both cryogel. Fourier transform infrared spectroscopy (FT-IR), scanning electron microscopy (SEM), thermal, surface area, elemental, and computerized microtomography (μCT) analyses were used for the characterization of cryogels.

Soil sustainable utilization technology: mechanism of flavonols in resistance process of heavy metal

The soil ecosystem is critical for agricultural production, affecting many aspects of human health. Soil has more unknown biodiversity and edaphic parameters than any other ecosystem especially when polluted. Metagenomics and metatranscriptomics were applied to research on toxicological characteristics of Pb and resistance mechanism of flavonols. Rhizosphere microorganisms-plants system, a unified system closely related to soil environment was taken as research object. Results emphasize gene expression changes in different test groups. Gene ontology enrichment and eggNOG showed that Pb has a toxic effect on gene and protein function which concentrated on ATPase and ATP-dependent activity. Differentially expressed genes in the flavonols group indicated that flavonols regulate amino acid transport and other transportation process related to Pb stress. Kegg analysis represents that Pb interferences energy production process via not only the upstream like glycolysis and tricarboxylic acid (TCA) circle but also oxidative phosphorylation process, which can also produce reactive oxygen species and impact the eliminating process. Flavonols have shown the ability in alleviating toxic effect of Pb and improving the resistance of plants. Flavonols can recover the electronic transmission and other process in TCA and oxidative phosphorylation via ascorbic acid-glutathione metabolism. Flavonols activated antioxidative process and non-specific immunity via vitamins B₂-B₆ metabolism.

Biochemical mechanism of phytoremediation process of lead and cadmium pollution with Mucor circinelloides and Trichoderma asperellum

This study focused on the bioremediation mechanisms of lead (0, 100, 500, 1000 mg kg^-1) and cadmium (0,10,50,100 mg kg^-1) contaminated soil using two indigenous fungi selected from mine tailings as the phytostimulation of Arabidopsis thaliana. The two fungal strains were characterized as Mucor circinelloides (MC) and Trichoderma asperellum (TA) by internal transcribed spacer sequencing at the genetic levels. Our research revealed that Cadmium was more toxic to plant growth than lead and meanwhile, MC and TA can strengthen A. thaliana tolerance to cadmium and lead with 40.19-117.50% higher root length and 58.31-154.14% shoot fresh weight of plant compared to non-inoculation. In this study, TA exhibited a higher potential to the inactivation of cadmium; however, MC was more effective in lead passivation. There was a direct correlation between the type of fungi, heavy metal content, heavy metal type and oxidative damage in plant. Both lead and cadmium induced oxidative damage as indicated by increased superoxide dismutase and catalase activities, while the antioxidant levels were significantly higher in fungal inoculated plants compared with those non-inoculated. The analysis of soil enzyme activity and taxonomic richness uncovered that the dominant structures of soil microbial community were altered by exogenous microbial agents. MC enhanced higher microbial diversity and soil enzyme activity than TA. The two indigenous fungi lessened several limiting factors with respect to phytoremediation technology, such as soil chemistry, contamination level and transformation, and metal solubility.

Facile Preparation of Tannic Acid-Poly(vinyl alcohol)/Sodium Alginate Hydrogel Beads for Methylene Blue Removal from Simulated Solution

A novel hydrogel bead [tannic acid (TA)-poly(vinyl alcohol) (PVA)/sodium alginate (SA)] with high strength prepared by biocompatible PVA, TA, and biocompatible SA via an instantaneous gelation method was applied to remove methylene blue (MB) from aqueous solution. The obtained TA-PVA/SA hydrogel beads were fully characterized by thermogravimetric analysis, Fourier-transform infrared spectroscopy, X-ray photoelectron spectroscopy, scanning electron microscopy, and so on. The adsorption performances of TA-PVA/SA hydrogel beads for MB were investigated by changing the factors of TA content, initial concentration, pH, adsorbent dosage, contact time, and temperature systematically. The maximum capacity of TA-PVA/SA hydrogel beads for MB removal was obtained to be 147.06 mg/g at 30 °C, whose capability was better than that without TA. After fitting the adsorbed data, it was basically consistent with the Langmuir isotherm and pseudo-second-order kinetic model. Thermodynamic studies indicated that MB removal was spontaneous and exothermic in nature. It is concluded that the low-cost TA-PVA/SA hydrogel beads as an easily recoverable adsorbent have a great potential on the removal of hazardous dyes from wastewater.

Acid pretreatment of three-dimensional graphite cathodes enhances the hydrogen peroxide synthesis in bioelectrochemical systems

Graphite is a potential catalyst for hydrogen peroxide (H₂O₂) synthesis in bioelectrochemical systems (BESs) because of its high performance and low cost. In this study, acidic pretreatment method was performed on raw graphite powder to optimize the performance of three-dimensional graphite cathode and increase the H₂O₂ yield. Through this method, the production rate of H₂O₂ increased by 46.9% after 20% nitric acid (HNO₃) pretreatment and reached up to 1.55 mg·L^-1·h^-1, while the chemical oxygen demand (COD) removal efficiency increased by 54%. The high micropore surface area of the acid-pretreated graphite cathode (23.32 m²·g) enhanced the oxygen reduction reaction (ORR) in the electrode and subsequently increased the Faradic efficiency and maximum power density by 25% and 45%, respectively. Thus, this approach has potential for H₂O₂ synthesis.

Enhanced lead and cadmium removal using biochar-supported hydrated manganese oxide (HMO) nanoparticles: Behavior and mechanism

Hydrated manganese oxide (HMO) nanoparticles were impregnated into a peanut shell-derived biochar (BC) to obtain a remarkable nanocomposite adsorbent, HMO-BC, which overcomes the technical barriers of singly applying either HMO or BC in practical heavy metal-containing wastewater treatment. HMO-BC can effectively sequestrate Pb(II) and Cd(II) in a wide pH range of 3-7 and exhibited more preferable sorption than bare BC in the presence of high-level competing cations. BC also significantly lowered the Mn leaching at acidic pH. Fixed-bed column adsorption tests showed that the effective treatment volume of HMO-BC for a simulated Pb(II)- or Cd(II)-laden wastewater is about 4-6 times higher than that of the BC host. In addition, HMO-BC was effective in removing Pb(II) from a real Pb-containing electroplating wastewater to discharge limit (0.2mgL^-1) with treatable volume of 525BV, much higher than that of the bare BC (60BV). More importantly, the saturated HMO-BC can be thoroughly regenerated for repeated uses without any observable capacity loss. Such attractive results of HMO-BC were attributed to the complementary effect of its two components. The embedded HMO nanoparticles provide preferable capture of target cations through specific inner-sphere complexation, as illustrated by XPS spectra of Pb 4f_7/2 and O1s, while the non-diffusive negatively charged oxygen-containing groups bound to BC facilitate the pre-enrichment and permeation of Pb(II) and Cd(II) cations into the pore channels prior to their preferable sorption through the Donnan membrane effect.

First-Principle Study of Li-Ion Storage of Functionalized Ti2C Monolayer with Vacancies

Two-dimensional transition metal carbides are notable as promising anode materials for Li-ion batteries (LIBs). Using first-principle calculations, we investigate the effect of vacancies on the Li adsorption and diffusion on Ti₂C and Ti₂CT₂ (where T denotes surface terminations, F or OH) monolayers. Interestingly, we find that the carbon vacancies (V_C) tend to enhance the adsorption of Li in Ti₂C monolayer, whereas the titanium vacancies (V_Ti) play a similar role in Ti₂CT₂ when functional groups present. The presence of vacancies further leads to a change in the diffusion behavior of Li atoms. In this context, we propose an idea to mitigate the adverse effects on Li diffusion performance by regulating the functional groups. In the presence of V_C, the surface of Ti₂C monolayer is suggested to be modified with OH- groups due to its relatively low diffusion barrier in the range of 0.025-0.037 eV when Li diffuses around V_C, whereas in the presence of V_Ti, the surface is suggested to remove the functional groups, resulting in a decrease of energy barrier by about 1 eV when Li atom diffuses around V_Ti. The present study may provide a guideline to improve the Li-ion storage performance of Ti₂C monolayers as electrode materials in LIBs, with atomic vacancies being taken into consideration.

Melting-assisted solvent-free synthesis of hierarchical SAPO-34 with enhanced methanol to olefins (MTO) performance

SAPO-34 zeolite with a butterfly patterned hierarchical pore system and high relative crystallinity was synthesized by a melting-assisted solvent-free route.