Functionalized CMK-3 mesoporous carbon with 2-amino-5-mercapto-1,3,4-thiadiazole for Hg(II) removal from aqueous media

Adsorption of heavy metals on natural zeolites: A review

Water pollution has jeopardized human health, and a safe supply of drinking water has been recognized as a worldwide issue. The increase in the accumulation of heavy metals in water from different sources has led to the search for efficient and environmentally friendly treatment methods and materials for their removal. Natural zeolites are promising materials for removing heavy metals from different sources contaminating the water. It is important to know the structure, chemistry, and performance of the removal of heavy metals from water, of the natural zeolites to design water treatment processes. This review focuses on critical analyses of the application of distinct natural zeolites for the adsorption of heavy metals from water, specifically, arsenic (As(III), As(V)), cadmium (Cd(II)), chromium (Cr(III), Cr(VI)), lead (Pb(II)), mercury(Hg(II)) and nickel (Ni(II)). The reported results of heavy-metal removal by natural zeolites are summarized, and the chemical modification of natural zeolites by acid/base/salt reagent, surfactants, and metallic reagents has been analyzed, compared, and described. Furthermore, the adsorption/desorption capacity, systems, operating parameters, isotherms, and kinetics for natural zeolites were described and compared. According to the analysis, clinoptilolite is the most applied natural zeolite to remove heavy metals. It is effective in removing As, Cd, Cr, Pb, Hg, and Ni. Additionally, an interesting fact is a variation between the natural zeolites from different geological origins regarding the sorption properties and capacities for heavy metals suggesting that natural zeolites from different regions of the world are unique.

Investigating Microcystin-LR adsorption mechanisms on mesoporous carbon, mesoporous silica, and their amino-functionalized form: Surface chemistry, pore structures, and molecular characteristics

Microcystin-LR (MC-LR) is the most common cyanotoxin released from algal-blooms. The study investigated the MC-LR adsorption mechanisms by comparing adsorption performance of protonated mesoporous carbon/silica (MC-H, MS-H) and their amino-functionalized forms (MC-NH₂ and MS-NH₂) considering surface chemistry and pore characteristics. The maximum MC-LR adsorption capacity (Langmuir model) of MC-H (37.87 mg/g) was the highest followed by MC-NH₂ (29.25 mg/g) and MS-NH₂ (23.03 mg/g), because pore structure is partly damaged during amino-functionalization. However, MC-NH₂ (k₂ = 0.042 g/mg/min) reacted faster with MC-LR than MC-H during early-stage adsorption due to enhancing electrostatic interactions. Intra-particle diffusion model fit indicated K_p,1 of MC-H (2.11 mg/g/min^1/2) was greater than MC-NH₂ due to its greater surface area and pore volume. Also, large mesopore diameters are favorable to MC-LR adsorption by pore diffusion. The effect of adsorbate molecular size on adsorption trend against MC-H, MC-NH₂ and MS-NH₂ was determined by kinetic experiments using two dyes, reactive blue and acid orange: MS-NH₂ achieved the highest adsorption for both dyes due to the large number of amino groups on its surface (41.2 NH₂/nm²). Overall, it was demonstrated that adsorption of MC-LR on mesoporous materials is governed by (meso-)pore diffusion and π - π (and hydrophobic) interactions induced by carbon materials; in addition, positively-charged grafted amino groups enhance initial MC-LR adsorption rate.

Sources, toxicity, and remediation of mercury: an essence review

Mercury (Hg) is a pollutant that poses a global threat, and it was listed as one of the ten leading 'chemicals of concern' by the World Health Organization in 2017. The review aims to summarize the sources of Hg, its combined effects on the ecosystem, and its remediation in the environment. The flow of Hg from coal to fly ash (FA), soil, and plants has become a serious concern. Hg chemically binds to sulphur-containing components in coal during coal formation. Coal combustion in thermal power plants is the major anthropogenic source of Hg in the environment. Hg is taken up by plant roots from contaminated soil and transferred to the stem and aerial parts. Through bioaccumulation in the plant system, Hg moves into the food chain, resulting in potential health and ecological risks. The world average Hg concentrations reported in coal and FA are 0.01-1 and 0.62 mg/kg, respectively. The mass of Hg accumulated globally in the soil is estimated to be 250-1000 Gg. Several techniques have been applied to remove or minimize elevated levels of Hg from FA, soil, and water (soil washing, selective catalytic reduction, wet flue gas desulphurization, stabilization, adsorption, thermal treatment, electro-remediation, and phytoremediation). Adsorbents such as activated carbon and carbon nanotubes have been used for Hg removal. The application of phytoremediation techniques has been proven as a promising approach in the removal of Hg from contaminated soil. Plant species such as Brassica juncea are potential candidates for Hg removal from soil.

Alkynyl carbon materials as novel and efficient sorbents for the adsorption of mercury(II) from wastewater

For the first time, a series of alkynyl carbon materials (ACMs) were prepared via the mechanochemical reaction of CaC₂ with six polyhalogenated precursors, namely CCl₄, C₂Cl₆, C₂Cl₄, C₆Cl₆, C₆Br₆, and C₁₄H₄Br₁₀ (ACM-1, ACM-2, ACM-3, ACM-4, ACM-5, and ACM-6, respectively) and used for the adsorptive removal of mercury from aqueous solutions. Based on preliminary investigations, the adsorption of mercury on ACM-5 was studied in depth. Specifically, the effect of pH on mercury adsorptivity, adsorption kinetics, thermodynamics, isotherms, and recyclability was studied. The adsorptivity of mercury on ACMs was found to be closely related to the hydrocarbon precursor, specific surface area of sorbent, and the alkynyl content. ACM-5 showed the best performance and is among the best raw carbonaceous sorbents reported so far, with a Langmuir saturated adsorption capacity of 191.9mgg^-1. The promising mercury adsorption performance mainly arises from the strong Lewis soft acid-soft base interactions between the alkynyl groups and mercury ions. The adsorption isotherms could be satisfactorily correlated with the Langmuir equation. The results show that the ACMs can be used as efficient sorbents for the removal of mercury and may also be useful for the adsorption of other heavy metals.

Highly Efficient Magnetic Nitrogen-Doped Porous Carbon Prepared by One-Step Carbonization Strategy for Hg2+ Removal from Water

Hydrophilic magnetic N-doped porous carbon composites (MNPCs) with high special surface areas and rich nitrogen content was prepared via simple one-step carbonization of zinc oxide nanoparticles (ZnO NPs), 2-methylimidazole (HmIm), and Fe₃O₄@SiO₂ magnetic nanoparticles (MNPs) mixture directly. During the carbonization process, ZnO NPs directly reacts with HmIm to yield porous ZIF-8 while the MNPs are incorporated into the frameworks to generate magnetic metal-organic frameworks (MFCs), and the MFCs acts as a self-sacrificing template to prepare MNPC. The obtained MNPCs via simple one-step carbonization strategy display higher adsorption capacity (429 mg g^-1) for Hg²⁺ ions than MNPC-T700-M3-T (382 mg g^-1) which was obtained by two-step synthesis strategy for comparison. It also exhibits very fast adsorption dynamics (adsorption rate constant (K₂) = 2.45 g mg^-1 min^-1) for Hg²⁺ and could efficiently remove 95% Hg²⁺ in 2 min for 20 mg L^-1 Hg²⁺ solution. Furthermore, the prepared MNPC exhibits good chemical stability and the adsorption capacity is still more than 95% even after 10 adsorption-elution cycles. The proposed method is easy-processing and economic, which not only provides highly efficient MNPCs for metal ions capture but also paves the ways toward various MFCs with different ligands through solvent/additive-free synthesis approaches.

Magnetic sulfur-doped porous carbon for preconcentration of trace mercury in environmental water prior to ICP-MS detection

A novel magnetic sulfur-doped porous carbon (MSPC) was fabricated via a simple one-step carbonization of a mixture of sucrose, basic magnesium sulfate whiskers and Fe₃O₄@SiO₂ nanoparticles.

Polyacrylonitrile-based fiber modified with thiosemicarbazide by microwave irradiation and its adsorption behavior for Cd(II) and Pb(II)

A novel thiosemicarbazide modified adsorbent (PAN(MW)-TSC) based on polyacrylonitrile fiber was successfully synthesized under microwave irradiation, which was applied for the uptake of Cd(II) and Pb(II) from aqueous solution subsequently. Microwave irradiation method is a new approach to achieve the modification and it turns out that just a 30min process is enough for the anchoring of functional groups in the fiber matrix. The surface characterization was performed by fourier transform infrared spectroscopy (FT-IR), scanning electron microscopy (SEM) elemental analysis (EA) and thermogravimetric analysis (TGA), indicating that the modification was successfully accomplished. Batch adsorption experiments including equilibrium isotherms, kinetics and the effects of pH and temperature on the adsorption of Cd(II) and Pb(II) were systematically studied. Among three kinetic models, the pseudo-second-order kinetic model provides the best correlation for the process. The nonlinear resolution of the Langmuir isotherm equation has been found to show the closest fit to the equilibrium date. Thermodynamic parameters, involving △G, △H and △S were also calculated from graphical interpretation of the experimental data, which suggest that metal ions adsorption onto PAN(MW)-TSC fibers is spontaneous and exothermic. Regeneration of PAN(MW)-TSC fibers loaded with metal ions was efficiently done with 0.5M HNO3, by which the investigated adsorbent could be used reproductively for five times with a small decrease in sorption capacity. The feasible preparation of PAN(MW)-TSC fibers with high adsorption capacities opens a new perspective in the potential application for wastewater treatment.

Removal of mercury by adsorption: a review

Due to natural and production activities, mercury contamination has become one of the major environmental problems over the world. Mercury contamination is a serious threat to human health. Among the existing technologies available for mercury pollution control, the adsorption process can get excellent separation effects and has been further studied. This review is attempted to cover a wide range of adsorbents that were developed for the removal of mercury from the year 2011. Various adsorbents, including the latest adsorbents, are presented along with highlighting and discussing the key advancements on their preparation, modification technologies, and strategies. By comparing their adsorption capacities, it is evident from the literature survey that some adsorbents have shown excellent potential for the removal of mercury. However, there is still a need to develop novel, efficient adsorbents with low cost, high stability, and easy production and manufacture for practical utility.

Highly dispersed cobalt oxide nanoparticles on CMK-3 for selective oxidation of benzyl alcohol

Nano cobalt oxide particles supported on ordered mesoporous carbon CMK-3 (CMK: carbon material from Korea) were prepared by a hydrothermal synthesis method.