Protein-derived nitrogen and sulfur co-doped carbon for efficient adsorptive removal of heavy metals

A nitrogen and sulfur co-doped carbon has been synthesized employing egg white as a sustainable protein-rich precursor. According to CHNS elemental analysis, N, S and O heteroatoms accounted for mass fractions of 3.66%, 2.28% and 19.29% respectively, and the types of surface functionalities were further characterized by FT-IR and XPS measurements. Although the carbon possessed a smaller surface area (815 m²·g^-1) compared to a commercial activated carbon (1100 m²·g^-1), its adsorption capacity towards Co²⁺ reached 320.3 mg·g^-1, which was over 8 times higher compared to the limited 34.0 mg·g^-1 over the activate carbon. Furthermore, the carbon was found to be an efficient adsorbent towards a series of metal ions including VO²⁺, Cr³⁺, Ni²⁺, Cu²⁺ and Cd²⁺. Combined with its environmental merits, the protein derived carbon may be a promising candidate for heavy metal pollution control.     

Sulfonated multi-walled carbon nanotubes for the removal of copper (II) from aqueous solutions

Sulfonated multi-walled carbon nanotubes (s-MWCNTs) was prepared from purified multi-walled carbon nanotubes (p-MWCNTs) by concentrated H₂SO₄ at elevated temperature. The structure was characterized by SEM, FTIR, Raman, XPS, and BET. It could be dispersed steadily in water at a dosage of 1.0 mg/mL for a week. The adsorption performance of s-MWCNTs toward Cu(II) was investigated including the effects of pH and ionic strength. Results indicated the adsorption was much dependent on pH but not on ionic strength. The adsorption capacity for Cu(II) was enhanced 58.9% via the sulfonation. Moreover, the adsorption mechanisms were carefully analyzed by Freundlich and D-R models.     

An overview of carbon nanotubes role in heavy metals removal from wastewater

The scarcity of water, mainly in arid and semiarid areas of the world is exerting exceptional pressure on sources and necessitates offering satisfactory water for human and different uses. Water recycle/reuse has confirmed to be successful and promising in reliable water delivery. For that reason, attention is being paid to the effective treatment of alternative resources of water (other than fresh water) which includes seawater, storm water, wastewater (e.g., dealt with sewage water), and industrial wastewater. Carbon nanotubes (CNTs) are called the technology of 21st century. Nowadays CNTs have been widely used for adsorption of heavy metals from water/ wastewater due to their unique physical and chemical properties. This paper reviews some recent progress (from 2013 to 2018) in the application of CNTs for the adsorption of heavy metals in order to remove toxic pollutants from contaminated water. CNTs are expected to be a promising adsorbent in the future because of its high adsorption potential in comparison to many traditional adsorbents.     

Adsorption characteristics of construction waste for heavy metals from urban stormwater runoff☆

Stormwater runoff has become an important source of surface water pollution. Bioretention, a low impact devel-opment measure in urban stormwater management, has been proven to be effective in the removal of pol utants from stormwater runoff, with appropriate bioretention media. In this study, construction wastes were selected as bioretention media to remove heavy metals from stormwater runoff. Static and dynamic adsorption batch exper-iments were carried out to investigate the adsorption of heavy metals in simulated stormwater runoff system with construction wastes in different particle sizes. The experimental results show that the pseudo-second-order kinetic model characterizes the adsorption process and the adsorption equilibrium data are wel described by Freundlich isotherm model. The construction wastes used can remove heavy metals from stormwater runoff effectively, with their average removal rates al more than 90%. The particle size of construction wastes greatly influences the equilibrium time, rate and adsorption capacity for heavy metals.     

A possibility of the production of carbon nanotubes from heavy hydrocarbons

A possibility of the production of carbon nanotubes from heavy hydrocarbon resources derived from natural asphalt was examined. Before the use of heavy hydrocarbons, pure compound, toluene was used as the pure substrate to establish the reaction system for the production of carbon nanotubes. Carbon nanotubes were found in the carbonaceous product deposited on inner wall of a quartz tube and at the exit of the tube. The carbonaceous product was observed by scanning electron microscopy and analyzed by temperature-programmed oxidation experiments to identify the presence of carbon nanotubes. Based on the reaction system and reaction conditions with toluene, the production of nanotubes was examined by using heavy hydrocarbons such as asphaltene and maltene fractions from a natural asphalt. Under selected reaction conditions including the reaction temperature and the amount of the catalyst, carbon nanotubes with a diameter of 30–60 nm were found.     

Removal of heavy metal ions from aqueous solution by multi-walled carbon nanotubes modified with 8-hydroxyquinoline: Kinetic study

Carbon nanotubes were modified with 8-hydroxyquinoline and used for the removal of Cu(II), Pb(II), Cd(II), and Zn(II) from aqueous solutions. Different instrumentation parameters and methods of development for determining metal ions from aqueous solutions using differential pulse anodic stripping voltammetry were studied. The adsorption of heavy metals from aqueous solution by the pristine and modified MWCNTs was studied kinetically using different kinetic models, and the results showed that the adsorption process best fitted the pseudo-second-order model and the Elovich model. The mechanism of adsorption was explored using the intra-particle diffusion model and the liquid-film model.     

Adsorption of zinc(II) from water with purified carbon nanotubes

Commercial single-walled carbon nanotubes (SWCNTs) and multi-walled carbon nanotubes (MWCNTs) were purified by sodium hypochlorite solutions and were employed as adsorbents to study the adsorption characteristics of zinc from water. The properties of CNTs such as purity, structure and nature of the surface were greatly improved after purification which made CNTs become more hydrophilic and suitable for adsorption of Zn²⁺. In general, the adsorption capacity of Zn²⁺ onto CNTs increased with the increase of pH in the pH range of 1-8, fluctuated very little and reached maximum in the pH range of 8-11 and decreased at a pH of 12. A comparative study on the adsorption of Zn²⁺ between CNTs and commercial powdered activated carbon (PAC) was also conducted. The maximum adsorption capacities of Zn²⁺ calculated by the Langmuir model are 43.66, 32.68, and with SWCNTs, MWCNTs and PAC, respectively, at an initial Zn²⁺ concentration range of 10-. The short contact time needed to reach equilibrium as well as the high adsorption capacity suggests that SWCNTs and MWCNTs possess highly potential applications for the removal of Zn²⁺ from water.     

Synthesis of a carbamide-based dithiocarbamate chelator for the removal of heavy metal ions from aqueous solutions

This study was carried out to develop a carbamide-based dithiocarbamate (CDTC) chelator for the removal of heavy metal ions from wastewater. Its structural properties were characterized by FT-IR, ¹H NMR and ¹³C NMR. Results confirmed the functional groups of HNC(S)S existed. The adsorption isotherms showed CDTC had a high adsorption capability for Zn (119.8 mg/g) and Cu (63.1 mg/g). It exhibited a distinctive selectivity for the removal of metal ions (Cu²⁺ > Zn²⁺ > Cr³⁺ > Pb²⁺ > Cd²⁺) as they coexisted. The influence of initial pH of wastewater for the removal efficiency of metal ions was also investigated and a pH > 7 was preferred.     

重金属离子脱除技术进展

综述了脱除水中重金属离子的各类主要方法 ,侧重介绍了近年来开发的若干新技术。     

生物法脱除污泥水中重金属的经济评价

针对美国农业部对农业使用污泥中重金属污染物的要求标准及达到上述标准的各种生物处理技术和简要流程,列举不同处理规模的各类生物处理流程的费用并进行了分析和经济评价,从而为用户选用污泥中重金属污染物处理的方案、设计和使用提供了详实而可靠的参考资料。     

Synthesis of magnetic Fe3O4@SiO2-(-NH2/-COOH) nanoparticles and their application for the removal of heavy metals from wastewater

In this work, Fe₃O₄@SiO₂-(-NH₂/-COOH) nanoparticles were synthesized for the removal of Cd²⁺, Pb²⁺ and Zn²⁺ ions from wastewater. The results of characterization showed that Fe₃O₄@SiO₂-(-NH₂/-COOH) was superparamagnetic with a core–shell structure. The surface of Fe3O4 was successfully coated with silica and modified with amino groups and carboxyl groups through the use of a silane coupling agent, polyacrylamide and polyacrylic acid. The dispersion of the particles was improved, and the surface area of the Fe3O4@SiO2-(-NH2/-COOH) nanoparticles was 67.8 m²/g. The capacity of Fe₃O₄@SiO₂-(-NH₂/-COOH) to adsorb the three heavy metals was in the order Pb²⁺ > Cd²⁺ > Zn²⁺, and the optimal adsorption conditions were an adsorption dose of 0.8 g/L, a temperature of 30°C and concentrations of Pb²⁺, Cd²⁺ and Zn²⁺ below 120, 80 and 20 mg/L, respectively. The maximum adsorption capacities for Pb²⁺, Cd²⁺ and Zn²⁺ were 166.67, 84.03 and 80.43 mg/g. The adsorption kinetics followed a pseudo-second-order model and Langmuir isotherm model adequately depicted the isotherm adsorption process. Thermodynamic analysis showed that the adsorption of the three metal ions was an endothermic process and that increasing the temperature was conducive to this adsorption.     

Superior adsorption performance of graphitic carbon nitride nanosheets for both cationic and anionic heavy metals from wastewater

Water pollution caused by highly toxic Cd(II), Pb(II), and Cr(VI) is a serious problem. In the present work,a green and low-cost adsorbent of g-C_3N_4 nanosheets was developed with superior capacity for both cationic and anionic heavy metals. The adsorbent was easily fabricated through one-step calcination of guanidine hydrochloride with thickness less than 1.6 nm and specific surface area of 111.2 m~2·g~(-1). Kinetic and isotherm studies suggest that the adsorption is an endothermic chemisorption process, occurring on the energetically heterogeneous surface based on a hybrid mechanism of multilayer and monolayer adsorption. The tri-s-triazine units and surface N-containing groups of g-C_3N_4 nanosheets are proposed to be responsible for the adsorption process.Further study on pH demonstrates that electrostatic interaction plays an important role. The maximum adsorption capacity of Cd(II), Pb(II), and Cr(VI) on g-C_3N_4 nanosheets is 123.205 mg·g~(-1), 136.571 mg·g~(-1),and 684.451 mg·g~(-1), respectively. The better adsorption performance of the adsorbent than that of the recently reported nanomaterials and low-cost adsorbents proves its great application potential in the removal of heavy metal contaminants from wastewater. The present paper developed a promising adsorbent which will certainly find applications in wastewater treatment and also provides guiding significance in designing adsorption processes.     

Additive manufacturing of sodalite monolith for continuous heavy metal removal from water sources

Herein, we present a simple strategy for preparing monolithic sodalite adsorbents via sequential additive manufacturing and post-treatments. In detail, the method includes (i) 3D printing of cylindrical monoliths using clay as the base material; (ii) thermal activation of the 3D-printed clay monoliths by calcination (to produce reactive alumina and silica species and enable mechanical stabilization); (iii) conversion of the activated clay monoliths to hierarchical porous sodalite monoliths via hydrothermal alkaline treatment. Parametric studies on the effect of calcination temperature, alkaline concentration and hydrothermal treatment time on the property of the resulting materials (such as phase composition and morphology) at different stages of preparation was conducted. Under the optimal conditions (i.e., calcination temperature of 850℃, NaOH concentration of 3.3 mol·L^-1, reaction temperature of 150℃, and reaction time of 6 h), a high-quality pure sodalite monolith was obtained, which possesses a relatively high BET surface area (58 m²·g^-1) and hierarchically micro-meso-macroporous structure. In the proposed application of continuous removal of heavy metals (chromium ion as the model) from wastewater, the developed 3D-printed sodalite monolith showed excellent Cr³⁺ removal performance and fast kinetics (~98% removal efficiency within 25 cycles), which outperformed the packed bed using sodalite pellets (made by extrusion).     

Adsorption performance of suitable nanostructured novel composite adsorbent of poly(N-methylaniline) for removal of heavy metal from aqueous solutions

Poly(N-methylaniline) (PNMA) composite composed of N-methylaniline and poly(ethanol) was prepared by in situ polymerization technique and characterized using FTIR, SEM-EDS and XRD instruments. Characterization of product revealed that this composite is crystalline in nature and the particles size is less than100 nm. The potential of this composite in removal of Cr(VI) ions from synthetic aqueous effluents was investigated by batch sorption system. The experimental results confirmed that this adsorbent has the potential application for removal of Cr(VI) ions from aqueous solution with the sorption capacity of 125 mg/g of Cr(VI)/0.1 g of adsorbent.     

Adsorption capacity and removal efficiency of heavy metal ions by Moso and Ma bamboo activated carbons

In order to understand the adsorption capacity and removal efficiency of heavy metal ions by Moso and Ma bamboo activated carbons, the carbon yield, specific surface area, micropore area, zeta potential, and the effects of pH value, soaking time and dosage of bamboo activated carbon were investigated in this study. In comparison with once-activated bamboo carbons, lower carbon yields, larger specific surface area and micropore volume were found for the twice-activated bamboo carbons. The optimum pH values for adsorption capacity and removal efficiency of heavy metal ions were 5.81–7.86 and 7.10–9.82 by Moso and Ma bamboo activated carbons, respectively. The optimum soaking time was 2–4 h for Pb²⁺, 4–8 h for Cu²⁺ and Cd²⁺, and 4 h for Cr³⁺ by Moso bamboo activated carbons, and 1 h for the tested heavy metal ions by Ma bamboo activated carbons. The adsorption capacity and removal efficiency of heavy metal ions of the various bamboo activated carbons decreased in the order: twice-activated Ma bamboo carbons > once-activated Ma bamboo carbons > twice-activated Moso bamboo carbons > once-activated Moso bamboo carbons. The Ma bamboo activated carbons had a lower zeta potential and effectively attracted positively charged metal ions. The removal efficiency of heavy metal ions by the various bamboo activated carbons decreased in the order: Pb²⁺ > Cu²⁺ > Cr³⁺ > Cd²⁺.     

Nitrate removal from water using functionalized carbon nanotube sheets

Carbon nanotube (CNT) sheets were synthesized via chemical vapor deposition of cyclohexanol and ferrocene in nitrogen atmosphere at 750 °C, functionalized using concentrated nitric acid and liquid ammonia and employed as adsorbents to study their nitrate adsorption characteristics. The results demonstrated that functionalization with nitrogen-containing groups improves nitrate adsorption capacity of the oxidized CNT sheets, significantly. Various isotherms and kinetic models were applied to fit the experimental data. Effects of contact time, initial nitrate concentration and adsorbent dosage were also investigated. Regeneration performance for the first time was also studied. For comparison, a similar study was performed with commercial activated carbon (AC). It was found out that the functionalized CNT sheets with higher nitrate adsorption capacity, shorter equilibrium time and better regeneration performance than AC, can be considered as potential adsorbents for nitrate removal from water in domestic applications.     

Removal of carbon disulfide (CS2) from water via adsorption on active carbon fiber (ACF)

The primary objective of this paper was to demonstrate the suitability of ACF in effectively adsorbing CS₂ from water, and to compare its performance vs. that of GAC. Commercial ACF was modified to increase its specific surface and pore volume. CS₂ removal was studied by adding ACF to water containing CS₂ under varying conditions. The experimental results reveal that ACF is a potential adsorbent for capturing CS₂ under both equilibrium and dynamic adsorption/desorption conditions. The adsorption capacity of ACF was observed to considerably increase with the increase of CS₂ concentration: It was observed that the modified ACF exhibited greater adsorption for CS₂ than the GAC, and the mechanism for this difference was explored; The modified ACF showed a consistent performance within a pH range from 3-9; Under the experimental conditions, an modified ACF sample was adsorbed and desorbed by boiling water repeatedly without exhibiting any appreciable degradation in its adsorption performance.     

碳纳米管对水体重金属污染物的吸附/解吸性能研究进展

详细阐述了碳纳米管(CNTs)对水体中和重金属离子的吸附/解吸影响因素和吸附机理,展望了碳纳米管在环境治理方面应用前景。     

Remove heavy metals from groundwater using carbon nanotubes grafted with amino compound

Multiwalled carbon nanotubes (MWCNTs) were modified with ethylenediamine tetraacetic acid (EDTA) with sufficient number of amino and carboxyl groups on the backbones and used for the removal of Fe(II) from aqueous solutions. Scanning electron microscopy, infrared spectroscopy, and X-ray showed the successful modification of the MWCNTs with EDTA. The adsorption parameters, such as temperature, pH and metal ion concentration, were determined using both Langmuir and Freundlich isotherm models. Surface complexation and ion exchange are the major removal mechanisms involved.     

Binary component sorption of Cu(II) and Pb(II) with activated carbon from Eucalyptus camaldulensis Dehn bark

The objective of this work is to illustrate the potential in the use of activated carbon in the binary component sorption of copper and lead ions. Eucalyptus bark was used as a precursor for the activated carbon which was prepared through the phosphoric acid activation process. This activated carbon was then used for the sorption of copper and lead ions. The quantity of the metal ions in the solution was measured with the Flame & Graphite Furnace Atomic Adsorption Spectrophotometer. The results indicated that the optimal pH for sorption was 5. The maximum sorption capacities for Cu(II) and Pb(II) were 0.45 and 0.53 mmol g⁻¹. Carboxylic, amine and amide groups were found to involve in the sorptions of Cu(II) and Pb(II). A major mechanism for the uptake of both heavy metals was proven not to be ion exchange but adsorption. In binary component sorptions, activated carbon still could sorb Pb(II) in a greater amount than Cu(II). However, the presence of the secondary metal ions suppressed the sorption of the primary metal ions. There seemed to have a linear inverse dependency between the sorption capacity and the concentration of the secondary metal ion.