Chemically functionalized silica gel with alkynyl terminated monolayers as an efficient new material for removal of mercury ions from water

Bio-grafted silica to make an asphalt road a sink for reactive environmental pollutants

Asphalt-surfaced areas such as roads have been reported as major non-combustion sources of reactive organic compounds in urban areas. Emission of latter compounds from asphalt is exacerbated due to exposure to sunlight and high temperature, contributing to negative human and environmental health outcomes. Furthermore, loss of asphalt components over time is linked to bitumen's aging that reduces service life of roads. Here, we introduce a designed bio-grafted-silica nano-filler derived from wood pellet as a sink for latter volatile compounds in an asphalt mixture. Molecular modeling calculations showed the remarkable adsorptive activity of the bio-grafted silica for trapping select asphalt volatiles, especially for the sulfur-containing aromatics and the oxygen-containing aromatics. Laboratory experiment revealed that the bitumen modified with bio-grafted silica exhibited up to 23% lower signs of aging. Thermogravimetric analysis proved that the modified bitumen exhibited a 16% reduction in mass loss compared to neat bitumen. Dynamic vapor sorption analysis also showed bio-grafted silica adsorbed higher amounts of a candidate volatile than pristine silica. The study outcomes highlights the advantages of a bio-derived modifier in asphalt to address concerns associated with the loss of hazardous compounds.

Highly efficient Hg2+ removal via a competitive strategy using a Co-based metal organic framework ZIF-67

The stronger coordination ability of mercury ions with organic ligands than the metal ions in metal organic framework (MOFs) provides an accessible way to separate mercury ions from solution using specific MOFs. In this study, a Co-based MOF (ZIF-67, Co(mIM)₂) was synthesized. It did not introduce specific functional groups, such as -SH and -NH₂, into its structure through complicated steps. It separate Hg²⁺ from wastewater with a new strategy, which utilized the stronger coordination ability of Hg²⁺ with the nitrogen atom on the imidazole ring of the organic ligand than the Co²⁺ ions. Hg²⁺ replaced Co²⁺ nodes from ZIF-67 and formed a more stable precipitate with mIM. The experimental results showed that this new strategy was efficient. ZIF-67 exhibited Hg²⁺ adsorption capacity of 1740 mg/g, much higher than the known MOFs sorbents. mIMs is the reaction center and ZIF-67 can improve its utilization. The sample color faded from purple to white due to the loss of cobalt ion. It is a great feature of ZIF-67 that allows users to judge whether the sorbent is deactivated intuitively. ZIF-67 can be sustainable recycled by adding organic ligands to the solution after treatment due to its simple synthesis method at room temperature. It's a high-efficient and sustainable sorbent for Hg²⁺ separation from wastewater.

Microwave-assisted functionalization of PAN fiber by 2-amino-5-mercapto-1,3,4-thiadiazol with high efficacy for improved and selective removal of Hg2+ from water

Mercury (Hg²⁺) contamination in water is associated with potential toxicity to human health and ecosystems. Many research studies have been ongoing to develop new materials for the remediation of Hg²⁺ pollution in water. In this study, a novel thiol- and amino-containing fibrous adsorbent was prepared by grafting 2-amino-5-mercapto-1,3,4-thiadiazol (AMTD) onto PAN fiber through a microwave-assisted method. The synthesized functional fiber was characterized by FTIR, SEM, and elemental analysis. Adsorption tests depicted that for mercury uptake, PAN_MW-AMTD fiber exhibited enhanced adsorption capacity compared with other fibrous adsorbents and selective adsorption feature under the interference of other metal ions, including Pb²⁺, Cu²⁺, Cd²⁺, and Zn²⁺. The influence of pH on the adsorption process was investigated and the effect of temperature revealed that the adsorption sorption process was endothermic and the adsorption performance of PAN_MW-AMTD was elevated with the increase of temperature. Kinetic studies of PAN_MW-AMTD fiber followed the pseudo-second-order and the adsorption isotherm of Hg²⁺ was well fitted by Sips and Langmuir equations, given the maximum adsorption amount of 332.9 mg/g. XPS results suggested that a synergetic coordination effect of sulfur and nitrogen in functional fiber with mercury took responsibility for the adsorption mechanism in the uptake process. In addition, the prepared PAN_MW-AMTD fiber could easily be regenerated with 0.1 M HCl for five times without significant reduction of mercury removal efficiency. Thus, this study will facilitate the research on novel functional material for the removal of mercury from water.

A Unique Interactive Nanostructure Knitting based Passive Sampler Adsorbent for Monitoring of Hg2+ in Water

This work reports the development of ultralight interwoven ultrathin graphitic carbon nitride (g-CN) nanosheets for use as a potential adsorbent in a passive sampler (PAS) designed to bind Hg²⁺ ions. The g-CN nanosheets were prepared from bulk g-CN synthesised via a modified high-temperature short-time (HTST) polycondensation process. The crystal structure, surface functional groups, and morphology of the g-CN nanosheets were characterised using a battery of instruments. The results confirmed that the as-synthesized product is composed of few-layered nanosheets. The adsorption efficiency of g-CN for binding Hg²⁺ (100 ng mL⁻¹) in sea, river, rain, and Milli-Q quality water was 89%, 93%, 97%, and 100%, respectively, at natural pH. Interference studies found that the cations tested (Co²⁺, Ca²⁺, Zn²⁺, Fe²⁺, Mn²⁺, Ni²⁺, Bi³⁺, Na⁺, and K⁺) had no significant effect on the adsorption efficiency of Hg²⁺. Different parameters were optimised to improve the performance of g-CN such as pH, contact time, and amount of adsorbent. Optimum conditions were pH 7, 120 min incubation time and 10 mg of nanosheets. The yield of nanosheets was 72.5%, which is higher compared to other polycondensation processes using different monomers. The g-CN sheets could also be regenerated up to eight times with only a 20% loss in binding efficiency. Overall, nano-knitted g-CN is a promising low-cost green adsorbent for use in passive samplers or as a transducing material in sensor applications.

Purification of starch and phosphorus wastewater using core-shell magnetic seeds prepared by sulfated roasting

Core-shell magnetic seeds with certain adsorption capacity that were prepared by sulfated roasting, served as the core of a magnetic separation technology for purification of starch wastewater. XRD and SEM results indicate that magnetite's surface transformed to be porous α-Fe₂O₃ structure. Compared with magnetite particles, the specific surface area was significantly improved to be 8.361 from 2.591 m²/g, with little decrease in specific susceptibility. Zeta potential, FT-IR and XPS experiments indicate that both phosphate and starch adsorbed on the surface of the core-shell magnetic seeds by chemical adsorption, which fits well with the Langmuir adsorption model. The porous surface structure of magnetic seeds significantly contributes to the adsorption of phosphate and starch species, which can be efficiently removed to be 1.51 mg/L (phosphate) and 9.51 mg/L (starch) using magnetic separation.

A novel monolith ZnS-ZIF-8 adsorption material for ultraeffective Hg (II) capture from wastewater

A novel monolithic adsorption material (ZnS-ZIF-8) was well prepared by means of the functionalized filter paper and explored for Hg (II) capture in wastewater in this work. The novel monolith ZnS-ZIF-8 displayed outstanding capture efficiency toward Hg (II) in the solution containing competitive diverse metal ions within very short time. The adsorption behavior was well fitted with the Langmuir adsorption model and the maximum adsorption capacities for Hg (II) removal was up to 925.9 mg/g. The Hg (II) captured by ZnS-ZIF-8 can be reclaimed by elution with Na₂S solution. The approach of this novel monolith adsorption material displayed the advantages of rapidity, simplicity, selectivity and could be expected to the development of a rapid and efficient device to purify Hg (II) from wastewater in form of the integration filter-adsorption column.

Facile Fabrication of 3D Graphene⁻Silica Hydrogel Composite for Enhanced Removal of Mercury Ions

Adsorption is a highly promising and widely used approach to remove Hg(II) ions from contaminated water. The key to this technology is exploring the effective adsorbent. The three-dimensional (3D) graphene as reduced graphene oxide hydrogel (rGH)-encapsulated silica gel (SG-PEI/rGH) was prepared by a moderate chemical reduction strategy using ascorbic acid. This composite structure was characterized by FTIR, XRD, and SEM analysis and used as adsorbents for Hg(II) ions. Its adsorption capacity toward Hg(II) ions was 266 mg/g and increased about 32% compared with the silica gel because of reduced graphene oxide hydrogel (rGH). Mechanism study showed that the high adsorption ability was due to the formation of an N–Hg complex with multi-amino groups on the surface of polyethyleneimine-modified silica gel (SG-PEI) and the rapid diffusion of adsorbed ions attributed to the rGH network structure. This composite SG-PEI/rGH would be a promising material for the removal of Hg(II) ions.

A new approach for the agglomeration and subsequent removal of polyethylene, polypropylene, and mixtures of both from freshwater systems - a case study

Based on a new concept for the sustainable removal of microplastics from freshwater systems, a case study for a pH-induced agglomeration and subsequent removal of polyethylene and polypropylene particles from water is presented. The two-step-based process includes firstly a localization and secondly an aggregation of microplastic particles (250-350 μM) in a physicochemical process. The research describes a strong increase in the particle size independent of pH of the aquatic milieu induced by the addition of trichlorosilane-substituted Si derivatives. The resulting Si-based microplastic aggregates (particle size after aggregation is 2-3 cm) could be easily removed by use of, e.g., sand traps. Due to the effect that microplastic particles form agglomeration products under every kind of process conditions (e.g., various pH, various polymer concentrations), the study shows a high potential for the sustainable removal of particles from wastewater.

Preparation of chitosan/MCM-41-PAA nanocomposites and the adsorption behaviour of Hg(II) ions

A novel functional hybrid mesoporous composite material (CMP) based on chitosan and MCM-41-PAA was reported and its application as an excellent adsorbent for Hg(II) ions was also investigated. Innovatively, MCM-41-PAA was prepared by using diatomite and polyacrylic acid (PAA) with integrated polymer-silica hybrid frameworks, and then CMP was fabricated by introducing MCM-41-PAA to chitosan using glutaraldehyde as a cross-linking agent. The structure and morphology of CMP were characterized by X-ray diffraction, Fourier transform infrared spectra, thermogravimetric analysis, scanning electron microscopy and Brunauer-Emmett-Teller measurements. The results showed that the CMP possessed multifunctional groups such as -OH, -COOH and -NH₂ with large specific surface area. Adsorption behaviour of Hg(II) ions onto CMP was fitted better by the pseudo-second-order kinetic model and the Langmuir model when the initial Hg(II) concentration, pH, adsorption temperature and time were 200 mg l^-1, 4, 298 K and 120 min, respectively, as the optimum conditions. The corresponding maximum adsorption capacity could reach 164 mg g^-1. According to the thermodynamic parameters determined such as free energy, enthalpy and entropy, the adsorption process of Hg(II) ions was spontaneous endothermic adsorption.

Coupling process study of lipid production and mercury bioremediation by biomimetic mineralized microalgae

Considering the high concentration of mercury in industrial wastewater, such as coal-fired power plants and gold mining wastewater, this research study investigated the coupling process of lipid production and mercury bioremediation using microalgae cells. Chlorella vulgaris modified by biomimetic mineralization. The cultivation was divided in two stages: a natural cultivation for 7days and 5days of Hg²⁺ addition (10-100μg/L) for cultivation at different pH values (4-7) after inoculation. Next, the harvested cells were eluted, and lipid was extracted. The fluorescein diacetate (FDA) dye tests demonstrated that the mineralized layer enhanced the biological activity of microalgae cells in Hg²⁺ contaminated media. Hg distribution tests showed that the Hg removal capacity of modified cells was increased from 62.85% to 94.74%, and 88.72% of eluted Hg²⁺ concentration was observed in modified cells compared to 48.42% of raw cells, implying that more mercury was transferred from lipid and residuals into elutable forms.

High removal efficacy of Hg(II) and MeHg(II) ions from aqueous solution by organoalkoxysilane-grafted lignocellulosic waste biomass

An effective organoalkoxysilanes-grafted lignocellulosic waste biomass (OS-LWB) adsorbent aiming for high removal towards inorganic and organic mercury (Hg(II) and MeHg(II)) ions was prepared. Organoalkoxysilanes (OS) namely mercaptoproyltriethoxylsilane (MPTES), aminopropyltriethoxylsilane (APTES), aminoethylaminopropyltriethoxylsilane (AEPTES), bis(triethoxysilylpropyl) tetrasulfide (BTESPT), methacrylopropyltrimethoxylsilane (MPS) and ureidopropyltriethoxylsilane (URS) were grafted onto the LWB using the same conditions. The MPTES grafted lignocellulosic waste biomass (MPTES-LWB) showed the highest adsorption capacity towards both mercury ions. The adsorption behavior of inorganic and organic mercury ions (Hg(II) and MeHg(II)) in batch adsorption studies shows that it was independent with pH of the solutions and dependent on initial concentration, temperature and contact time. The maximum adsorption capacity of Hg(II) was greater than MeHg(II) which respectively followed the Temkin and Langmuir models. The kinetic data analysis showed that the adsorptions of Hg(II) and MeHg(II) onto MPTES-LWB were respectively controlled by the physical process of film diffusion and the chemical process of physisorption interactions. The overall mechanism of Hg(II) and MeHg(II) adsorption was a combination of diffusion and chemical interaction mechanisms. Regeneration results were very encouraging especially for the Hg(II); this therefore further demonstrated the potential application of organosilane-grafted lignocellulosic waste biomass as low-cost adsorbents for mercury removal process.

One-step fabrication and characterization of a poly(vinyl alcohol)/silver hybrid nanofiber mat by electrospinning for multifunctional applications

Preparation and application of a poly(vinyl alcohol)/silver hybrid nanofiber mat by electrospinning.