Removal of aqueous-phase lead ions by dithiocarbamate-modified hydrochar

Adsorption of Cu (II) and Zn (II) in aqueous solution by modified bamboo charcoal

Due to the development of industries such as mining, smelting, industrial electroplating, tanning, and mechanical manufacturing, heavy metals were discharged into water bodies seriously affecting water quality. Bamboo charcoal, as an environmentally friendly new adsorbent material, in this paper, the virgin bamboo charcoal (denoted as WBC) was modified with different concentrations of KMnO4 and NaOH to obtain KMnO4-modified bamboo charcoal (KBC) and NaOH-modified bamboo charcoal (NBC) which was used to disposed of water bodies containing Cu2+ and Zn2+. The main conclusions were as following: The adsorption of Cu2+ by WBC, KBC and NBC was significantly affected by pH value, and the optimum pH was 5.0. Differently, the acidity and alkalinity of the solution doesn't effect the adsorption of Zn2+ seriousely. Meanwhile, surface diffusion and pore diffusion jointly determine the adsorption rate of Cu2+ and Zn2+. The test result of EDS showed that Mn-O groups formed on the surface of K6 (WBC treated by 0.06 mol/L KMnO4) can promote the adsorption of Cu2+ and Zn2+ at a great degree. The O content on N6(WBC treated by 6 mol/L NaOH) surface increased by 30.95% compared with WBC. It is speculated that the increase of carbonyl group on the surface of NBC is one of the reasons for the improvement of Cu2+ and Zn2+ adsorption capacity. Finally, the residual concentrations of Cu2+ and Zn2+ in wastewater are much lower than 0.5 mg/L and 1.0 mg/L, respectively. Thus it can be seen, KBC and NBC could be a promising adsorbent for heavy metals.

Competitive adsorption of heavy metals onto xanthate-modified sludge hydrochar and its solidification as secondary minerals

In this study, a sulfur-modified magnetic hydrochar was synthesized by grafting thiol-containing groups onto the sludge-derived hydrochar. The modified hydrochar exhibited effective adsorption of Cu2+, Pb2+, Zn2+, and Cd2+ over a wide pH range and in the presence of coexisting ions, and showed almost no secondary leaching in three acidic solutions. In the mult-metal ion system, the modified hydrochar exhibited maximum adsorption capacities were 39.38, 105.74, 26.53, and 38.11 mg g-1 for Cu2+, Pb2+, Zn2+, and Cd2+, respectively. However, the binding capacity and adsorption amount of modified hydrochar for metal ions were lower in the mult-metal ion system compared to the unit-metal ion system. Notably, Pb2+ showed a strong inhibitory effect on the adsorption of other heavy metal ions by modified hydrochar due to strong competition for xanthate functional groups. The Pb2+ occupied the xanthate and native functional groups (-OH, -NH2, and Fe-O etc.), leaving only a small amount of adsorption sites for Cu2+, Zn2+ and Cd2+. Simulation results further supported these findings, indicating that Pb2+ had the highest density profiles near the four functional groups, and the density profiles of the four heavy metals near the xanthate functional groups were greater compared to the other three functional groups. Furthermore, the SEM-EDS, TOF-SIMI, and XPS results indicated that modified hydrochar achieved excellent mineral binding mainly through electrostatic interaction, ion exchange, and chelation. Overall, these results highlight the sulfur-modified magnetic hydrochar as a highly efficient adsorbent for heavy metals in environmental applications.

Towards Negative Emissions: Hydrothermal Carbonization of Biomass for Sustainable Carbon Materials

The contemporary production of carbon materials heavily relies on fossil fuels, contributing significantly to the greenhouse effect. Biomass is a carbon-neutral resource whose organic carbon is formed from atmospheric CO2. Employing biomass as a precursor for synthetic carbon materials can fix atmospheric CO2 into solid materials, achieving negative carbon emissions. Hydrothermal carbonization (HTC) presents an attractive method for converting biomass into carbon materials, by which biomass can be transformed into materials with favorable properties in a distinct hydrothermal environment, and these carbon materials have made extensive progress in many fields. However, the HTC of biomass is a complex and interdisciplinary problem, involving simultaneously the physical properties of the underlying biomass and sub/supercritical water, the chemical mechanisms of hydrothermal synthesis, diverse applications of resulting carbon materials, and the sustainability of the entire technological routes. This review starts with the analysis of biomass composition and distinctive characteristics of the hydrothermal environment. Then, the factors influencing the HTC of biomass, the reaction mechanism, and the properties of resulting carbon materials are discussed in depth, especially the different formation mechanisms of primary and secondary hydrochars. Furthermore, the application and sustainability of biomass-derived carbon materials are summarized, and some insights into future directions are provided.

Insight into stability of dithiocarbamate-modified adsorbents: Oxidation of dithiocarbamate

We previously reported that monoalkyl dithiocarbamate-modified cellulose (DMC) exhibited excellent adsorption performance for arsenite (AsIII), cadmium (CdII), lead (PbII), gold (AuIII), silver (AgI), platinum (PtIV), and palladium (PdII). However, its adsorption capability for AsIII decreased by 96.4% after two weeks of storage at 40 °C under an air atmosphere. This decrease in adsorption ability could occur for other metals that dithiocarbamates can extract. In this study, we investigated the adsorption performance of DMC for various metals before and after storage and proposed a possible mechanism for this decrease. We found significant decreases in the adsorption abilities of PbII (11.4%), AgI (39.5%), PtIV (65.5%), and PdII (69.6%), whereas AuIII and CdII adsorption was largely retained, with decreases of 1.1% and 4.0%, respectively. FTIR analysis of the stored DMC revealed the formation of S-S bonds and the retention of dithiocarbamate peaks, indicating the formation of dithiocarbamate dimers (thiuram disulfides). To further support thiuram disulfide formation, dialkyl thiuram disulfides were tested for the adsorption of the seven employed metals. The metal adsorption behavior of dialkyl thiuram disulfides was almost identical to that of the stored adsorbent, ensuring thiuram disulfide formation. In conclusion, the loss of adsorption capability can be mainly attributable to the formation of thiuram disulfide.

Trithiocyanurate-functionalized hydrochar for effectively removing methylene blue and Pb (II) cationic pollutants

Functionalization can change the physicochemical properties of hydrochar and improve its ability to adsorb pollutants. Herein, a trithiocyanurate-functionalized hydrochar (TTHC) was obtained from acylation of chloroacetyl chloride and hydrochar and modification with trithiocyanuric acid in alkaline conditions. TTHC can efficiently remove cationic methylene blue (MB) and Pb(II) from wastewater. The removal can be expressed with pseudo-second-order kinetic and Langmuir models. The MB and Pb(II) removed uptakes by TTHC at 298 K exceeded 909.9 and 182.8 mg g-1 respectively, and the removal rates reached 90% and 98% within 120 min respectively. Characterizations show TTHC is functionalized with trithiocyanurate, and rich in thiolate and aromaticity, and tends to adsorb MB/Pb(II) via multiple adsorption mechanisms. After five sorption-desorption regeneration cycles, TTHC maintained 80% and 99% adsorption capacities for MB and Pb(II) respectively. Therefore, TTHC is a promising efficient sorbent for removing MB and Pb(II) from effluents.

Synthesis of a Novel Dithiocarbamate Surfactant Derivative Adsorbent for Efficient Removal of Heavy Metal Ions

In this work, a novel heavy metal chelating agent (DTC-SDS) containing dithiocarbamate (DTC) was synthesized using sodium dodecyl sulfate (SDS), formaldehyde, and carbon disulfide. DTC-SDS has excellent trapping performance under pH 1-7 and initial concentrations 100-500 mg/L. With the increase in adsorbent dose, the adsorption amount of DTC-SDS increases and then decreases, and the optimized dosage of DTC-SDS is 0.02 g. The DTC-SDS adsorbent exhibits superior adsorption capacity (191.01, 111.7, and 79.14 mg/g) and high removal rates (97.99%, 98.48%, and 99.91%) for Mn2+, Zn2+, and Pb2+ respectively, in wastewater. Such remarkable adsorption performance could be attributed to the strong trapping effect on heavy metal ions by the C-S bond of DTC-SDS. The liquid adsorbent was in full contact with heavy metal ions, which further enhanced the complexation of heavy metal ions. The adsorption isothermal model showed that the adsorption process was typical of Langmuir monomolecular layer adsorption. Kinetic studies showed that the pseudo-second-order kinetic model fits the experimental adsorption data better than the pseudo-first-order kinetic model. In the ternary metal species system (Mn2+, Zn2+, and Pb2+), DTC-SDS preferentially adsorbed Pb2+ due to its highest covalent index. The main controlling step is the chemical interaction between the active groups of DTC-SDS and the heavy metal ions. This work provides valuable insights into the adsorption of heavy metal ions onto dithiocarbamate, which could guide the development of other heavy metal chelating agents and be beneficial for developing novel treatments of wastewater contaminated with heavy metals.

A review on adsorption of heavy metals from wastewater using carbon nanotube and graphene-based nanomaterials

The rampant rise in world population, industrialization, and urbanization expedite the contamination of water sources. The presence of the non-biodegradable character of heavy metals in waterways badly affects the ecological balance. In this modern era, the unavailability of getting clear water as well as the downturn in water quality is a major concern. Therefore, the effective removal of heavy metals has become much more important than before. In recent years, the attention to better wastewater remediation was directed towards adsorption techniques with novel adsorbents such as carbon nanomaterials. This review paper primarily emphasizes the fundamental concepts, structures, and unique surface properties of novel adsorbents, the harmful effects of various heavy metals, and the adsorption mechanism. This review will give an insight into the current status of research in the realm of sustainable wastewater treatment, applications of carbon nanomaterials, different types of functionalized carbon nanotubes, graphene, graphene oxide, and their adsorption capacity. The importance of MD simulations and density functional theory (DFT) in the elimination of heavy metals from aqueous media is also discussed. In addition to that, the effect of factors on heavy metal adsorption such as electric field and pressure is addressed.

Adsorption of lead ions and methylene blue on acrylate-modified hydrochars

Hydrochars are promising sorbents for wastewater treatment. Herein, two acrylate-modified hydrochars (AMHC₁ and AMHC₂) were obtained by grafting acrylic acid on the surface of two hydrochars (MHC₁ and MHC₂ hydrothermally carbonized in water and acidic medium respectively) with free radical polymerization. Characterizations show that MHC₂ is more prone to free radical polymerization than MHC₁ does, and has higher carboxylate content after modification. The adsorption amounts of AMHC₂ over methylene blue (MB) and Pb(II) are much higher than those of AMHC₁. Pseudo-second-order kinetic and Langmuir isotherm equations well fit the Pb(II) and MB sorption data of AMHC₂. The Pb(II) adsorptive mechanism is mainly inner-surface complexation accompanied by ion exchange and cation-π interaction. MB adsorption involves ion exchange, electrostatic interaction, H-bonding and π-π interaction. Hence, the one-step modification method of free radical polymerization under alkaline condition has great potential for preparing carboxylate-modified hydrochars to adsorb cationic pollutants.

Selective recovery of Cu(II) from strongly acidic wastewater by zinc dimethyldithiocarbamate: Affecting factors, efficiency and mechanism

The selective recovery of copper from strongly acidic wastewater containing mixed metal ions remains a significant challenge. In this study, a novel reagent zinc dimethyldithiocarbamate (Zn(DMDC)₂) was developed for the selective removal of Cu(II). The removal efficiency of Cu(II) reached 99.6% after 120 min reaction at 30°C when the mole ratio Zn(DMDC)₂/Cu(II) was 1:1. The mechanism investigation indicates that the Cu(DMDC)₂ products formed as a result of the displacement of Zn(II) from the added Zn(DMDC)₂ by Cu(II) in wastewater, due to the formation of stronger coordination bonds between Cu(II) and the dithiocarbamate groups of Zn(DMDC)₂. Subsequently, we put forward an innovative process of resource recovery for strongly acidic wastewater. Firstly, the selective removal of Cu(II) from actual wastewater using Zn(DMDC)₂, with a removal efficiency of 99.7%. Secondly, high-value CuO was recovered by calcining the Cu(DMDC)₂ at 800°C, with a copper recovery efficiency of 98.3%. Moreover, the residual As(III) and Cd(II) were removed by introducing H₂S gas, and the purified acidic wastewater was used to dissolve ZnO for preparation of valuable ZnSO₄·H₂O. The total economic benefit of resource recovery is estimated to be 11.54 $/m³. Accordingly, this study provides a new route for the resource recovery of the treatment of copper-containing acidic wastewater.

Highly efficient removal of Pb2+ from wastewater by a maleic anhydride modified organic porous adsorbent

Sorption is prominent in low price, high efficiency, availability, and eco-friendliness. Organic porous materials have the characteristics of easy functionalization, diverse structure and stability, and show great potential in adsorption, energy storage, catalysis, and other fields. A mesoporous phenolic resin-type polymer (PRP) was successfully synthesized and modified by solid state reaction with maleic anhydride to prepare adsorbent (called as PRP-MAH) for sorption of Pb²⁺. The impact of reaction conditions (the pH value, reaction temperature, fresh concentration of solution, ionic strength and reaction time, etc.) was systematically studied. Characterization methods such as SEM, FTIR, and XPS indicated that the synthesized adsorbent PRP-MAH had regular morphology and good stability. The fitting of isothermal adsorption experiment data conforms to Langmuir sorption isotherm, and the sorption capacity reached 366.40 mg·g^-1 at 308 K. The kinetic data were consistent with the quasi-second-order model, which indicated that the chemisorption might play the main role in the sorption process. Thermodynamic research manifested that the sorption of Pb²⁺ by PRP-MAH was carried out by a spontaneous process at the study temperature. The studies show that PRP-MAH can remove Pb²⁺ from water solution through ion exchange, electrostatic attraction, and surface complexation.

Hydrothermal conversion of biomass to fuels, chemicals and materials: A review holistically connecting product properties and marketable applications

Biomass is a renewable and carbon-neutral resource with good features for producing biofuels, biochemicals, and biomaterials. Among the different technologies developed to date to convert biomass into such commodities, hydrothermal conversion (HC) is a very appealing and sustainable option, affording marketable gaseous (primarily containing H₂, CO, CH₄, and CO₂), liquid (biofuels, aqueous phase carbohydrates, and inorganics), and solid products (energy-dense biofuels (up to 30 MJ/kg) with excellent functionality and strength). Given these prospects, this publication first-time puts together essential information on the HC of lignocellulosic and algal biomasses covering all the steps involved. Particularly, this work reports and comments on the most important properties (e.g., physiochemical and fuel properties) of all these products from a holistic and practical perspective. It also gathers vital information addressing selecting and using different downstream/upgrading processes to convert HC reaction products into marketable biofuels (HHV up to 46 MJ/kg), biochemicals (yield >90 %), and biomaterials (great functionality and surface area up to 3600 m²/g). As a result of this practical vision, this work not only comments on and summarizes the most important properties of these products but also analyzes and discusses present and future applications, establishing an invaluable link between product properties and market needs to push HC technologies transition from the laboratory to the industry. Such a practical and pioneering approach paves the way for the future development, commercialization and industrialization of HC technologies to develop holistic and zero-waste biorefinery processes.

Comprehensive study on the hydrochar for adsorption of Cd(II): preparation, characterization, and mechanisms

Hydrothermal carbonization process via converting invasive plants into functional materials may provide a novel strategy to comprehensively control and utilized the exotic invasive plants. In this study, Eupatorium adenophorum was utilized to fabricate the hydrochar via hydrothermal carbonization process, which was further applied to remove Cd(II). The results showed that the hydrochar was a mesoporous material with abundant O-containing functional groups (OFPs) on the surface. The adsorption isotherms were fitted by both the Langmuir and Freundlich models, and the maximum adsorption amount achieved 24.53 mg/g. The adsorption dynamics were governed by surface adsorption and film diffusion. pH and ionic strength can exert a strong influence on the adsorption efficiency. The mechanisms on the adsorption of Cd(II) on the hydrochar concluded the pore-filling effects, electrostatic interactions, ion exchange, precipitation, coordination with π electrons, and surface complexation with the OFPs, such as hydroxyl, carboxylic, phenol, acetyl, and ester groups. Thus, hydrothermal carbonization process may provide a promising technique to fabricate the hydrocar for the treatment of Cd(II), which may facilitate comprehensive control of invasive plants and boost to the carbon neutrality.

Interactions between Cr(VI) and the hydrochar: The electron transfer routes, adsorption mechanisms, and the accelerating effects of wood vinegar

Conversion of the low-valued invasive plant biomass into high-grade carbonaceous materials may provide a novel strategy to tackle the global issues of climate changes and exotic plant invasion. In this study, the hydrochar was fabricated from the biomass of Eupatorium adenophorum spreng. via hydrothermal carbonization (HTC) process to remove Cr(VI). The adsorption thermodynamics and kinetics were investigated via batch experiments, and the electron transfer routes and adsorption mechanisms were further revealed based on systematic characterization. The adsorption isotherms were well fitted by the Langmuir model with a maximum adsorption amount of 7.76 mg/g. The adsorption was spontaneous, and the surface adsorption and intraparticle diffusion may be the speed-limiting steps. Both -OH group and furan structures may donate the electrons to reduce Cr(VI), and the adsorption was governed by the surface complexation with the oxygen-containing functional groups including hydroxyl and carboxyl. Furthermore, the wood vinegar, as the by-product, can significantly accelerate the reduction rate of Cr(VI). Thus, this study provided a new strategy to fabricate carbonaceous materials which may facilitate to boost the carbon neutrality and control of invasive plants.

Pyrolysis temperature affects the physiochemical characteristics of lanthanum-modified biochar derived from orange peels: Insights into the mechanisms of tetracycline adsorption by spectroscopic analysis and theoretical calculations

Biochar (BC) derived from orange peels was modified using LaCl₃ to enhance its tetracycline (TC) adsorption capacity. SEM-EDS, FT-IR, XRD, and BET were used to characterize the physiochemical characteristics of La-modified biochar (La-BC). Batch experiments were conducted to investigate the effects of several variables like pyrolysis temperature, adsorbent dosage, initial pH, and coexisting ions on the adsorption of TC by La-BC. XPS and density functional theory (DFT) were used to elucidate the TC adsorption mechanism of La-BC. The results demonstrated that La was uniformly coated on the surface of the La-BC. The physiochemical characteristics of La-BC highly depended on pyrolysis temperature. Higher temperature increased the specific surface area and functional groups of La-BC, thus enhancing its TC adsorption capacity. La-BC prepared at 700 °C (BC@La-700) achieved the maximum adsorption capacity of 143.20 mg/g, which was 6.8 and 4.6 times higher than that of BC@La-500 and BC@La-600, respectively. The mechanisms of TC adsorption by La-BC were most accurately described by the pseudo-second-order kinetic model. Furthermore, the adsorption isotherm of La-BC was consistent with the Freundlich model. BC@La-700 achieved good TC adsorption efficiencies even at a wide pH range (pH 4-10). Humic acid significantly inhibited TC adsorption by La-BC. The presence of coexisting ions (NH₄⁺, Ca²⁺, NO₃^-) did not significantly affect the adsorption capacity of La-BC, particularly BC@La-700. Moreover, BC@La-700 also exhibited the best recycling performance, which achieved relative high adsorption capacity even after 5 cycles. The XPS results showed that π-π bonds, oxygen-containing functional groups, and La played a major role in the adsorption of TC on La-BC. The result of DFT showed that the adsorption energy of La-BC was the greatest than that of other functional groups on biochar. Collectively, our findings provide a theoretical basis for the development of La-BC based materials to remove TC from wastewater.

Opportunities for Recycling PV Glass and Coal Fly Ash into Zeolite Materials Used for Removal of Heavy Metals (Cd, Cu, Pb) from Wastewater

This work shows the development and characterization of two zeolite structures by recycling PV glass and coal fly ash for the removal of cadmium, copper, and lead from synthetic solutions containing one or three cations. The materials were characterized in terms of crystalline structure (XRD), morphology (SEM, AFM), and specific surface. For increasing the heavy-metals removal efficiency, the adsorption conditions, such as substrate dosage, preliminary concentration, and contact time, were optimized. The pseudo-second-order kinetic model adsorption kinetics fit well to describe the activity of the zeolites ZFAGPV-A and ZFAGPV-S. The zeolite adsorption equilibrium data were expressed using Langmuir and Freundlich models. The highest adsorption capacities of the ZFAGPV-A zeolite are q_maxCd = 55.56 mg/g, q_maxCu = 60.11 mg/g, q_maxPb = 175.44 mg/g, and of ZFAGPV-S, are q_maxCd = 33.45 mg/g, q_maxCu = 54.95 mg/g, q_maxPb = 158.73 mg/g, respectively. This study demonstrated a new opportunity for waste recycling for applications in removing toxic heavy metals from wastewater.

Calcium-pyro-hydrochar derived from the spent mushroom substrate as a functional sorbent of Pb2+ and Cd2+ from aqueous solutions

A calcium-pyro-hydrochar (Ca-PHC) can be distinguished as a novel sorbent of Pb²⁺ and Cd²⁺ from an aqueous solution. It was obtained using hydrothermal treatment of the spent mushroom substrate (SMS), followed by a CaCl₂·5H₂O activation and pyrolysis. The characterisation of chars before and after modifications was done by scanning electron microscope (SEM), Brunauer-Emmett-Teller (BET) and Fourier transform infrared (FTIR). Batch experiments were performed to examine Ca-PHC's sorption properties and binding mechanisms to selected metal ions. The maximum sorption capacities of Ca-PHC for Pb²⁺ and Cd²⁺ were 297 mg g^-1, and 131 mg g^-1, respectively. The obtained results demonstrated that the sorption of Pb²⁺ and Cd²⁺ by Ca-PHC follows a pseudo-second kinetic model and Freundlich isotherm. The binding of the selected metals onto Ca-PHC was enabled by the ion-exchange mechanism, surface complexation, mineral precipitation and cation-π interaction. Thermodynamic parameters indicate that metal ions binding by Ca-PHC are spontaneous and endothermic. Due to the high adsorption capacities, the obtained Ca-PHC has good potential for application in industrial wastewater treatment. In addition, the demonstrated use of SMS highlights another possibility of applying this specific biomass relevant to sustainable and economical waste management in the growing mushroom industry.

Synthesis of polyaminophosphonated-functionalized hydrochar for efficient sorption of Pb(II)

Surface modification can effectively improve the ability of hydrochar to capture pollutants from wastewater. In this work, polyaminophosphonated-functionalized hydrochar (PAP-HC) was successfully synthesized by a chemical grafting approach and applied efficiently to adsorb aqueous Pb(II). Properties of PAP-HC were characterized by ICP, FTIR, XPS, SEM-EDS, elemental analysis, zeta potential, and BET. The Pb(II) adsorbing behavior of PAP-HC was tested by batch adsorbing assays, including the pH impact, uptake kinetics, sorption isotherms, sorption thermodynamics, and PAP-HC recycling. Sorption isotherms were better illustrated by a Langmuir equation, while the kinetic profile was modeled by a pseudo-second-order equation. Adsorption of Pb(II) onto PAP-HC mainly relied on chelating Pb(II) with aminophosphonate groups of PAP-HC by XPS and FTIR analyses. The actual adsorbed amount of PAP-HC maximized to 179.92 mg·g^-1 at 298 K, which showed high adsorption ability. Nitric acid and hydroxide solutions were suitable for desorption of adsorbed Pb(II) and activated PAP-HC, respectively. PAP-HC can be reused for at least five cycles without obvious change in adsorption performance. The results suggest PAP-HC is a prospective adsorbent to capture Pb(II) from wastewater.

Enhanced removal of Cr(VI) by cation functionalized bamboo hydrochar

Chemical modification on hydrochars can significantly improve their ability of removing heavy metal ions from wastewater, but so far no research has focused on the chemical modification through free radical reaction. In this work, a cation functionalized hydrochar (CFHC) bearing - N⁺H₂R was synthesized by grafting-polymerization of glycidyl methacrylate (GMA) onto bamboo hydrochar under initiation by benzoyl peroxide, followed by the amination with the introduced epoxy group and diethylenetriamine and a subsequent hydrochloric acid treatment. The resulted CFHC exhibited a superior removal capacity of 424.09 mg·g^-1 for Cr(VI), and the highest sorption occurred at pH of 2. Combining a series of characterizations and tests, it was concluded that the sorption conformed to the pseudo-second-order and Freundlich equations, indicating a multilayer chemisorption process that mainly driven by electrostatic reaction, reduction, and surface complexation. This research proved that a free radical polymerization treatment could effectively transform hydrochars into super adsorbents for wastewater treatment.

The Versatility in the Applications of Dithiocarbamates

Dithiocarbamate ligands have the ability to form stable complexes with transition metals, and this chelating ability has been utilized in numerous applications. The complexes have also been used to synthesize other useful compounds. Here, the up-to-date applications of dithiocarbamate ligands and complexes are extensively discussed. Some of these are their use as enzyme inhibitor and treatment of HIV and other diseases. The application as anticancer, antimicrobial, medical imaging and anti-inflammatory agents is examined. Moreover, the application in the industry as vulcanization accelerator, froth flotation collector, antifouling, coatings, lubricant additives and sensors is discussed. The various ways in which they have been employed in synthesis of other compounds are highlighted. Finally, the agricultural uses and remediation of heavy metals via dithiocarbamate compounds are comprehensively discussed.

Controllable synthesis of bifunctional corn stalk cellulose as a novel adsorbent for efficient removal of Cu2+ and Pb2+ from wastewater

A corn stalk cellulose-based adsorbent with bifunctional groups of -NH-/-NH₂ and C-S/C=S for efficient removal of Cu²⁺ and Pb²⁺ was successfully synthesized. Under specific alkali and reaction conditions, 4.58 mmol/g of C-S/C=S groups were further introduced on surface of aminated cellulose with 6.99 mmol/g of amino groups. The introduced CS₂ would only participate in the esterification with -NH₂ groups to form special dithiocarbamate (DTC) structures containing -NH- groups (-NHCS₂^-). The synthesized DTC structures would not reduce total amount of -NH-/-NH₂ groups on aminated cellulose to keep its excellent adsorption performance for Cu²⁺, and the introduced appropriate number of C-S/C=S groups could ensure the efficient removal of Pb²⁺. It was suitable for removal of coexisting Cu²⁺ and Pb²⁺ with low initial concentration in real wastewater, and the removal rates were both close to 100%. The application of the bifunctional cellulose offered a novel way for purpose of 'waste treatment by waste'.

Modified Activated Carbon for Copper Ion Removal from Aqueous Solution

Because of increasing environmental awareness, it is becoming more important to remove harmful elements from water solutions. This study used activated carbon (AC) derived from waste wood-based panels as the base material, oxidized with nitric acid (OAC), and grafted with iminodiacetic acid (IDA-OAC) to improve the adsorption capacity and affinity for metals. The characterization of AC, OAC, and IDA-OAC was conducted via FTIR, SEM, N2 adsorption and desorption analysis, elemental analysis, Boehm titration, and point of zero charge (PZC). The instrument studies proved the modified increasing of the functional groups of the adsorbents. Moreover, batch and column experiments were conducted to evaluate the ability of the three adsorbents to remove copper ions from aqueous solution. In batch sorption, IDA-OAC had the highest adsorption capacity (84.51 mg/g) compared to OAC (54.74 mg/g) and AC (24.86 mg/g) at pH 5. The breakthrough point (Ct/Ci = 0.05) of copper ions for IDA-OAC occurred much later than AC in the column experiment (AC = 19 BV, IDA-OAC = 52 BV). The Langmuir isotherm and pseudo-second-model kinetics modeling could better fit with the data obtained from the batch sorption of AC, OAC, and IDA-OAC. The significant capacity and reusability of IDA-OAC displayed high applicability for water treatment.

Synthesis of tri-metallic surface engineered nanobiochar from cynodon dactylon residues in a single step - Batch and column studies for the removal of copper and lead ions

Superparamagnetic nanocomposites integrated with multiple metals, and surface engineered nanoparticles play a vital role in the removal of heavy metals. In the present study, amino-functional silica-coated magnetic nanocomposites with biochar synthesised from Cynodon dactylon plant residues are prepared in a single step reaction process. The synthesised nanocomposites are characterized using various analytical techniques such as FTIR to determine their functional entities, SEM, TEM, EDX and VSM to analyse the size (~50 nm), elements and magnetic nature of the nanocomposites. Characterization reveals that the prepared nanobiochar was coated with silica and a specific amine group. The magnetic saturation value of 50 emu/g confirms the prepared sorbent was superparamagnetic. Kinetics, isotherm and thermodynamics parameters are evaluated to study the metal interaction mechanism with the nanocomposites where the system follows pseudo-second-order kinetics and the four-parameter Fritz Schlunder model for both metal ions. The nanocomposites showed the enhanced adsorption capacity of copper (Cu(II)) ions with 220.4 mg/g and 185.4 mg/g for lead (Pb(II)) ions. The nanocomposites also showed the excessive reusing ability of 15 times with the maximum removal efficiency for Cu(II) and Pb(II) metal ions. Column studies are evaluated to demonstrate the vital performance in the removal of Cu(II) ions and the breakthrough point was inferred for the parameters such as concentration (100-300 mg/L), bed height (1-3 cm) and flow rate (2-4 mL/min). The breakthrough point was attained at 1400 min and the removal efficiency of about 64.58% was obtained.

Hydrothermal Carbonization of Residual Algal Biomass for Production of Hydrochar as a Biobased Metal Adsorbent

Conversion of residual algal biomass to value-added products is essential for enhancing the economics of algae cultivation. Algal hydrochar produced via hydrothermal carbonization of lipid-extracted Picochlorum oculatum is a material rich in oxygen functional groups and carbon (up to 67.3%) and hence a promising candidate for remediation of wastewaters. The hydrothermal carbonization conditions were optimized and the adsorption capacity of the hydrochar was tested for metal removal. By the end of the remediation process, cumulative removal of Al3+, Cu2+, Fe2+, Mg2+, Mn2+, and Pb2+ reached 89, 98, 75, 88, 75, and 100%, respectively. The adsorption of all metals was found to follow pseudo second-order kinetics and the Langmuir isotherm. Overall, when hydrothermal carbonization is applied to lipid-extracted algae, it generates a promising biobased adsorbent with value-added potential in metal remediation.

Enhanced removal of Cr(VI) by nitrogen-doped hydrochar prepared from bamboo and ammonium chloride

N-doped biochar can effectively eliminate toxic Cr(VI). Here, N-doped hydrochar (NHC) was successfully synthesized by one-pot hydrothermal carbonization (HTC) of NH₄Cl and bamboo, and employed to adsorb Cr(VI). The specific surface area, pore volume, and carbon and nitrogen contents of NHC all increase compared with the undoped hydrochar (HC). NH₄Cl acts as a cheap nitrogen source to enhance the nitrogen content of hydrochar and as an acid catalyst to accelerate hydrochar carbonization. Adsorption experiments show NHC has higher adsorption capacity than HC for Cr(VI). XPS and FTIR imply the dominant mechanisms of adsorbing Cr(VI) onto two hydrochars are electrostatic attraction, reduction and complexation, but the contributions of surface functional groups in two hydrochars for elimination of Cr(VI) differ. The doped nitrogen in NHC is pivotal in adsorbing and reducing Cr(VI). Hence, NHC prepared from bamboo and NH₄Cl by one-step HTC is a cheap and efficient adsorbent to eliminate aqueous Cr(VI).

Ultrafast and efficient removal of Pb(II) from acidic aqueous solution using a novel polyvinyl alcohol superabsorbent

The direct removal of heavy metal ions from acidic wastewater is a hard problem. In this study, a novel superabsorbent, polyvinyl alcohol phosphate ester (PVAP), was designed and prepared to remove Pb(II) from acidic wastewater (pH = 3). The PVAP can absorb water and swell to reach equilibrium within 30 s, which provides the conditions for ultrafast kinetic adsorption. For 100 mg/L Pb(II) solution, the adsorption reaches equilibrium within 5 min, and the removal ratio is more than 99.9% over a wide pH range of 3-6. Adsorption kinetics and isotherm data are consistent with pseudo-second-order and Langmuir model, respectively. The calculated maximum adsorption capacity for Pb(II) is 558.66 mg/g. Thermodynamic results show that the adsorption is spontaneous and exothermic process. The removal ratio for Pb(II) of PVAP still maintains above 99% after ten recycles. The PVAP can also simultaneously remove more than 97% of other heavy metal ions (Cu(II), Cd(II), Zn(II), Co(II), and Ni(II)) from an acidic solution. Moreover, the PVAP can efficiently purify simulated acid mine heavy metal wastewater, and the results meet EPA drinking water standards. The studies of X-ray photoelectron spectroscopy (XPS) and Fourier transform infrared (FT-IR) spectroscopy prove that the adsorption mechanism involves surface complexation. This new superabsorbent is a promising candidate for acidic heavy metal sewage disposal.

Interpret the elimination behaviors of lead and vanadium from the water by employing functionalized biochars in diverse environmental conditions

Wide-ranging researches have been executed to treat groundwater from different mining areas, although complex behaviors of diverse metal ion species in the groundwater have not been illustrated clearly. This research study explored the mechanisms through which Pb(II) and V(V) are eliminated in single and binary-metal removal processes by oxygen, nitrogen, and sulfur-doped biochars also considering the kinetic and characterization techniques. The adsorption efficiency of V (V) was enhanced by oxygen-doped biochar at pH 4 with an adsorption capacity of ~70 mg/g. However, Pb (II) was rapidly removed at pH 6 with a higher adsorption capacity of ~180 mg/g by the nitrogen and sulfur-doped biochar forming PbCO3 and V(CO)6 crystals along the single-metal removal process. These results could be explained by the Hard Soft Acid Base theory. The hard Lewis acid vanadium was attracted by the hard Lewis base oxygen, and the intermediate Lewis acid lead was attracted by the intermediate and soft Lewis base nitrogen and sulfur. Besides, the removal ability of Pb(II) and V(V) in the binary-metal removal process showed a similar phenomenon for all types of biochars at pH 4 with the adsorption capacity of ~400 mg/g for Pb(II) and 175 mg/g for V(V), but the composition of vanadium species remains unclear on the surface of the biochars. Initially, H3V2O7-, H2VO4-, and HVO42- species were electrostatically attracted by the oxygen-based functionalities, then V(V) species was partially reduced to VO2+ by the oxygen, nitrogen, and sulfur functionalities in different ratios. Finally, H3V2O7-, H2VO4-, and HVO42- species produced Pb5(VO4)3Cl and Pb2V2O7 which co-precipitate with Pb(II), but VO2+ does not generate any form of precipitates. The above-explained technique supports the treatment of vanadium mining groundwater with valuable vanadinite (Pb5(VO4)3Cl) mineral.

Efficient removal of Pb(II) ions from aqueous solution by modified red mud

In the work, we employed a hydrothermal method for modification of red mud using colloidal silica and sodium hydroxide under mild conditions, and applied it into adsorbing Pb(II) ions in aqueous solutions. In the modification, zeolite structure was formed. The adsorption experiments found that the adsorption capacity of the modified red mud for Pb(II) ions was significantly improved, almost 10 times as much as that of the original red mud. Both the pseudo-first-order and pseudo-second-order kinetic equation can describe the adsorption process, indicating it a more complicated interaction. Langmuir and Dubinin-Radushkevich models well fit the adsorption isotherm, indicating that the modified red mud mainly removes lead ions from aqueous solution by monolayer physical adsorption. According to the fitting results, the saturated adsorption capacity of Pb (II) by the modified red mud is 551.11 mg/g, confirming its high efficiency adsorption performance. XRD, FTIR, XPS and SEM-EDS all detected the formation of PbCO₃ and Pb₃(CO₃)₂(OH)₂. It was speculated that the adsorption mechanism should be attributed to the joint contribution of ion exchange and precipitation. The excellent performance of the modified red mud on Pb(II) ions adsorption makes it a promising candidate for the treatment of wastewater contaminated by heavy metal ions.

High effective adsorption of Pb(II) from solution by biochar derived from torrefaction of ammonium persulphate pretreated bamboo

Biochar was prepared by torrefaction of ammonium persulphate pretreated bamboo (labeled as APBC) and applied into elimination of Pb(II) from water solutions. APBC was characterized by N₂ adsorption-desorption isotherms, elemental and Zeta potential analyses, SEM-EDS, XPS, and FTIR. Abundant N- and O-containing groups appeared atop APBC. Batch sorption assays revealed that APBC had high affinity and strong sorption ability towards Pb(II). The high Pb(II) adsorbing ability was attributed to the high contents of N- and O-containing functional groups of APBC. The adsorption mechanism mainly occurred by inner-sphere surface complexation. Hence, torrefaction of ammonium persulphate pretreated bamboo is a promising strategy for producing efficient biochar that is applicable for industrial wastewater treatment.

Hydrochar and pyrochar for sorption of pollutants in wastewater and exhaust gas: A critical review

Pollutants in wastewater and exhaust gas bring out serious concerns to public health and the environment. Biochar can be developed as a sustainable adsorbent originating from abundant bio-wastes, such as agricultural waste, forestry residue, food waste and human waste. Here we highlight the state-of-the-art research progress on pyrochar and hydrochar for the sorption of pollutants (heavy metal, organics, gas, etc) in wastewater and exhaust gases. The adsorption performance of pyrochar and hydrochar are compared and discussed in-depth, including preparation procedures (carbonization and activation), sorption possible mechanisms, and physiochemical properties. Challenges and perspective for designing efficient and environmental benign biochar-based adsorbents are finally addressed.

Dithiocarbamate-modified cellulose-based sorbents with high storage stability for selective removal of arsenite and hazardous heavy metals

A series of cellulose derivatives bearing dialkyl dithiocarbamate (DTC) groups were synthesized. Their ability of sorption of arsenite (As(iii)) and heavy metals and their storage stability in the solid state were investigated. Among them, DTC-modified cellulose derived from l-proline showed the highest sorption capacity for As(iii) and heavy metals to selectively remove them from aqueous media. It also showed exellent storage stability in air at 40 °C.

Dithiocarbamate-modified cellulose derived from l-proline works as a storable sorbent for selective removal of toxic As(iii) and heavy metals from aqueous media.