Recovery of heavy metal complexes from wastewaters: A critical review of mechanisms and technologies

Heavy metal complexes (HMCs) pose significant ecological challenges while also holding attractive economic value. This review comprehensively summarizes advanced techniques for recovering HMCs from wastewater, including reductive recovery, oxidative decomplexation-recovery, and non-redox separation. Physical and chemical separation approaches utilize specific properties of metal complexes for efficient segregation. Specifically, we explore oxidative decomposition techniques, emphasizing the underlying mechanisms and practical application for selective and non-selective decomplexation techniques. The crucial role of cathodic potential on the efficiency and selectivity of electrochemical reduction processes is also examined. In addition, a comprehensive cost assessment, including energy consumption, associated with these recovering processes is investigated, and opinions on the inadequacy of current studies are provided. Overall, this review uniquely integrates findings on selective physical separation, oxidation, and reduction processes as well as the cost assessments for these techniques, providing a novel and comprehensive perspective on heavy metal recovery. It aims to bridge existing gaps in literature and advance the development of effective recovery methodologies for HMCs.

Preparation of high-performance adsorption carbon materials via hydrothermal carbonization of agricultural solid waste-grapevines

This study uses grapevine agricultural waste to prepare grapevine-derived biobased activated carbon (AGV) through chemical activation with NaOH after hydrothermal carbonization. A comprehensive analysis of the adsorption performance and mechanisms of AGV for methylene blue (MB) was conducted. The results demonstrated that AGV possesses a highly developed reticular pore structure, with a specific surface area of 3230.57 m2 g-1 and is rich in oxygen functional groups (OFGs). At pH 7.0, AGV achieved a removal rate of 90 % within 30 min, with a maximum adsorption capacity of 661.7 mg g-1, surpassing that of most previously reported activated carbons. Adsorption followed the Langmuir isotherm and pseudo-second-order kinetics, with thermodynamics confirming endothermic and spontaneous MB adsorption. The adsorption mechanism primarily involves chemical adsorption, including electrostatic interactions, pore filling, hydrogen bonding, acid-base interactions, and π-π stacking. The AGV maintained 86.7 % adsorption efficiency after 5 cycles, demonstrating excellent recyclability. This study provides a novel approach for preparing high-performance adsorption materials from waste biomass.

Recent advances in the synthesis and application of graphene aerogel and silica aerogel for environment and energy storage: A review

Aerogel materials have gained considerable attention in recent years due to their promising applications in environmental and energy storage fields, owing to their exceptional properties, including high porosity, ultra-low thermal conductivity, low density, and high specific surface area. This review begins by examining novel synthesis techniques, including sol-gel processing, chemical crosslinking, and templating, that enhance both the microstructural and functional properties of aerogels. Next, we explore the applications of graphene and silica aerogels in environmental and energy conservation technologies. Graphene aerogels, in particular, demonstrate significant potential in water purification by effectively removing antibiotics, offering a new approach to water treatment. The combination of silica aerogels with phase change materials, along with their use in supercapacitors, demonstrates their potential for energy conservation. Additionally, we discuss the synergistic effects of silica and graphene aerogels, which further broaden their applications. Finally, the paper concludes by summarizing the potential of graphene and silica aerogels as functional materials for environmental applications and outlining the challenges and future directions for their development and industrial use.

Advancements in iron-based photocatalytic degradation for antibiotics and dyes

The accelerated growth of the economy and advancements in medical technology have led to the discharge of a diverse range of organic pollutants into water sources. Recent investigations into water treatment have demonstrated the potential for integrating photocatalysis with techniques such as photocatalytic persulfate activation and the Photo-Fenton process for more efficient wastewater management. Iron-based photocatalysts responsive to visible light offer several advantages, including non-toxicity, safety, affordability, and excellent chemical and optical properties. Currently, there is a notable increase in research activity focused on the iron-based photocatalytic degradation of antibiotics and dyes. Given their abundance, cost-effectiveness, and eco-friendliness, iron-based photocatalysis shows considerable promise for various applications, including water treatment, air purification, and energy conversion. The use of iron-based photocatalysts has been demonstrated to facilitate the production of more reactive oxygen radicals, achievable through the Photo-Fenton process, direct photocatalysis, and the photocatalytic activation of persulfates. This approach has been demonstrated to enhance the degradation efficiency of antibiotics and dyes. Ongoing research encompasses the preparation and refinement of iron-based materials, exploration of photocatalytic mechanisms, and expansion of practical applications. Future directions include material innovation, elucidation of mechanisms, scaling up applications, and multifunctionalization, with the objective of enhancing photocatalytic efficiency, transitioning the technology from laboratory settings to practical scales, and providing effective solutions to environmental challenges and energy constraints.

Evaluation and mechanistic analysis of the effect of the addition of alkaline earth metal CaO on Cd solidification enhancement in lightweight aggregate preparation

The volatilization of Cd during the preparation of lightweight aggregates (LWAs) can cause serious damage to the environment, so a method to harmlessly transform Cd during this process is required. In this regard, the alkaline earth metal CaO was added to Cd-containing aggregate raw materials for treatment, and the effect of CaO addition on the properties of LWAs in the presence of chlorine and sulfate was investigated. Kinetic models of the Cd volatilization were established by using the Arrhenius equation to predict the volatilization of Cd at different sintering stages. The results showed that 0.8% wt of CaO under the influence of chlorine can reduce the Cd volatilization rate from 84.9% to 12.64%, corresponding to an increase in the reaction activation energy (E a) from 22.62 to 49.55 kJ mol-1. Additionally, the Cd volatilization rate under the influence of sulfate was reduced from 30% to 8%, with an increase in the E a from 33.25 to 42.62 kJ mol-1. The activation energy increase suggests that the addition of CaO is beneficial because it increases the energy required for Cd volatilization. According to the Cd leaching experiments conducted on the LWAs, it was found that the solidification ratio of Cd was higher than 99.9% for all samples after the addition of CaO. The addition of CaO promotes the formation of CdFe2O4 and anorthite for effective solidification of Cd, thus optimizing the structures of the LWAs. This work may provide a new idea for Cd waste recycling.

A tremella-like in situ synthesis of ZIF-67Co(OH)F@Co3O4 on carbon cloth as an electrode material for supercapacitors

In this study, a simple in situ technique followed by hydrothermal method is used to synthesize a novel tremella-like structure of ZIF-67Co(OH)F@Co3O4/CC metal-organic framework (MOF) derived from zeolite imidazole. The in situ synthesis of metal-organic frameworks (MOFs) increases their conductivity and produces more active sites for ion insertion. Their unique, scalable design not only provides more space to accommodate volume change but also facilitates electrolyte penetration into the electrode resulting in more active materials being utilized and ion-electron transfer occurring faster during the cycle. As a result, the binder-free ZIF-67Co(OH)F@Co3O4/CC supercapacitor electrode exhibits typical pseudo-capacitance behaviour, with a specific capacitance of 442 F g-1 and excellent long-term cycling stability of 90% after 5000 cycles at 10 A g-1.

Nickel vanadate nitrogen-doped carbon nanocomposites for high-performance supercapacitor electrode

A nickel-vanadium-based bimetallic precursor was produced using the polymerization process by urea-formaldehyde copolymers. The precursor was then calcined at 800 °C in an argon ambiance to form a Ni3V2O8-NC magnetic nanocomposite. Powerful techniques were used to study the physical characteristics and chemical composition of the fabricated Ni3V2O8-NC electrode. PXRD, Raman, and FTIR analyses proved that the crystal structure of Ni3V2O8-NC included N-doped graphitic carbon. FESEM and TEM analyses imaging showed the distribution of the Ni3V2O8 nanoparticles on the layered graphitic carbon structure. TEM images showed the prepared sample has a particle size of around 10-15 nm with an enhanced active site area of 146 m2/g, as demonstrated by BET analysis. Ni3V2O8-NC nanocomposite exhibits magnetic behaviors and a magnetization saturation value of 35.99 emu/g. The electrochemical (EC) studies of the synthesized Ni3V2O8-NC electrode proceeded in an EC workstation of three-electrode. In a 5 M potassium hydroxide as an electrolyte, the cyclic voltmeter exhibited an enhanced capacitance (CS) of 915 F/g at 50 mV/s. Galvanic charge-discharge (GCD) study also exhibited a superior capacitive improvement of 1045 F/g at a current density (It) of 10 A/g. Moreover, the fabricated Ni3V2O8-NC nanocomposite displays a good power density (Pt) of 356.67 W/kg, improved ion accessibility, and substantial charge storage. At the high energy density (Et) of 67.34 W h/kg, the obtained Pt was 285.17 W/kg. The enhanced GCD rate, cycle stability, and Et of the Ni3V2O8-NC magnetic nanocomposite nominate the sample as an excellent supercapacitor electrode. This study paves the way for developing effective, efficient, affordable, and ecologically friendly electrode materials.

Critical Aspects of Various Techniques for Synthesizing Metal Oxides and Fabricating Their Composite-Based Supercapacitor Electrodes: A Review

Supercapacitors (SCs) have attracted attention as an important energy source for various applications owing to their high power outputs and outstanding energy densities. The electrochemical performance of an SC device is predominantly determined by electrode materials, and thus, the selection and synthesis of the materials are crucial. Metal oxides (MOs) and their composites are the most widely used pseudocapacitive SC electrode materials. The basic requirements for fabricating high-performance SC electrodes include synthesizing and/or chemically modifying unique conducting nanostructures, optimizing a heterostructure morphology, and generating large-surface-area electroactive sites, all of which predominantly rely on various techniques used for synthesizing MO materials and fabricating MO- and MO-composite-based SC electrodes. Therefore, an SC’s background and critical aspects, the challenges associated with the predominant synthesis techniques (including hydrothermal and microwave-assisted syntheses and chemical-bath and atomic-layer depositions), and resulting electrode electrochemical performances should be summarized in a convenient, accessible report to accelerate the development of materials for industrial SC applications. Therefore, we reviewed the most pertinent studies on these synthesis techniques to provide insight into the most recent advances in synthesizing MOs and fabricating their composite-based SC electrodes as well as to propose research directions for developing MO-based electrodes for applications to next-generation SCs.

Facile synthesis of efficient construction of tungsten disulfide/iron cobaltite nanocomposite grown on nickel foam as a battery-type energy material for electrochemical supercapacitors with superior performance

In this research literature, a tungsten disulfide/iron cobaltite (WS₂/FeCo₂O₄) interwoven construction array was prepared by a simplistic hydrothermal approach on Ni foam as an integrative electrode for supercapacitors (SCs). For characterization of the wearing of WS₂ nanostructure on FeCo₂O₄ nanosheets (WS₂/FeCo₂O₄) by the Scanning electron microscope (SEM), transmission electron microscope (TEM), X-ray diffraction (XRD), and X-ray photoelectron spectroscopy (XPS). The WS₂/FeCo₂O₄ nanosheets supply a larger surface region and sufficient space to allow for volume changes. Moreover, considerable features of wellbeing conductivity from the Ni foam conductor and the synergistic procedures between WS₂ and FeCo₂O₄, the integrated WS₂/FeCo₂O₄ composite achieved prominent SCs storage performances with a higher specific capacity of 1122C g^-1 (2492.9F g^-1) at 1 A g^-1 and notable capacity retention of 98.1% at 3 A g^-1 after 5000 long cycles and retained higher rate capacity of 951.9 C g^-1 at 15 A g^-1. For practical application, an asymmetric supercapacitors type WS₂/FeCo₂O₄//active carbon (WS₂/FeCo₂O₄//AC) device was successfully prepared. The WS₂/FeCo₂O₄//AC device displays a higher specific capacity of 110C g^-1 and energy density of 85.68 W h kg^-1 at power density at 897.65 W kg^-1, as well as the superior initial capacitance of 98.7% with cyclic stabilities after 4000 long cycles. Thus, these results indicated the great potential of the constructed WS₂/FeCo₂O₄//AC in the scenario electrochemical properties due to their outstanding energy storage activities.

Electrochemical biosensor based on CuPt alloy NTs-AOE for the ultrasensitive detection of organophosphate pesticides

The electrode material is vital for the performance of the electrochemical biosensor. Lately, many nanomaterials have been developed to improve the sensitivity and detection efficiency of the biosensors. In this work, a kind of one-dimensional nanomaterials, the CuPt alloy nanotubes with an open end (CuPt alloy NTs-AOE), was explored. The nanotubes with an open end can provide a larger electrochemical active surface area and more active sites for the immobilization of enzyme. The CuPt alloy displays excellent conductivity and catalytic activity. In addition, the Cu shows the great affinity to thio-compounds, which can greatly enhance the detection efficiency and sensitivity. As a result, the prepared biosensor demonstrates the wider linear range of 9.98 × 10^-10-9.98 × 10^-5g l^-1for fenitrothion and 9.94 × 10^-11-9.94 × 10^-4g l^-1for dichlorvos (as model OPs ) and with the lower detection limit of 1.84 × 10^-10g l^-1and 6.31 × 10^-12g l^-1(S/N = 3), respectively. Besides, the biosensor has been used to detect the real samples and obtains satisfactory recoveries (95.58%-100.56%).

Advanced materials and technologies for supercapacitors used in energy conversion and storage: a review

Supercapacitors are increasingly used for energy conversion and storage systems in sustainable nanotechnologies. Graphite is a conventional electrode utilized in Li-ion-based batteries, yet its specific capacitance of 372 mA h g−1 is not adequate for supercapacitor applications. Interest in supercapacitors is due to their high-energy capacity, storage for a shorter period and longer lifetime. This review compares the following materials used to fabricate supercapacitors: spinel ferrites, e.g., MFe2O4, MMoO4 and MCo2O4 where M denotes a transition metal ion; perovskite oxides; transition metals sulfides; carbon materials; and conducting polymers. The application window of perovskite can be controlled by cations in sublattice sites. Cations increase the specific capacitance because cations possess large orbital valence electrons which grow the oxygen vacancies. Electrodes made of transition metal sulfides, e.g., ZnCo2S4, display a high specific capacitance of 1269 F g−1, which is four times higher than those of transition metals oxides, e.g., Zn–Co ferrite, of 296 F g−1. This is explained by the low charge-transfer resistance and the high ion diffusion rate of transition metals sulfides. Composites made of magnetic oxides or transition metal sulfides with conducting polymers or carbon materials have the highest capacitance activity and cyclic stability. This is attributed to oxygen and sulfur active sites which foster electrolyte penetration during cycling, and, in turn, create new active sites.