Single- and multi-component adsorption of cadmium and zinc using activated carbon derived from bagasse--an agricultural waste

Recent Advances in Carbonaceous Photocatalysts with Enhanced Photocatalytic Performances: A Mini Review

Photocatalytic processes based on various semiconductors have been widely utilized in different applications, with great potential for use in environmental pollution remediation and sustainable energy generation. However, critical issues, including low light adsorption capability, wide energy bandgap, and unsatisfactory physicochemical stability still seriously limit the practical applications of photocatalysts. As a solution, the introduction of carbonaceous materials with different structures and properties into a photocatalyst system to further increase the activity has attracted much research attention. This mini review surveys the related literatures and highlights recent progress in the development of carbonaceous photocatalysts, which include various metal semiconductors with activated carbon, carbon dots, carbon nanotubes/nanofibers, graphene, fullerene, and carbon sponges/aerogels. Moreover, graphitic carbon nitride is also discussed as a carbon-rich and metal-free photocatalyst. The recently developed synthesis strategies and proposed mechanisms underlying the photocatalytic activity enhancement for different applications are summarized and discussed. Finally, ongoing challenges and the developmental direction for carbonaceous photocatalysts are proposed.

Study of pre-treatment of quinoline in aqueous solution using activated carbon made from low-cost agricultural waste (walnut shells) modified with ammonium persulfate

Activated carbon made from agricultural waste (walnut shells) was investigated as a suitable adsorbent for effectively removing quinoline from industrial wastewater. The activated carbon was treated with phosphoric acid and oxidized by ammonium persulfate and its ability to adsorb pyridine and quinoline in aqueous solution was investigated. Kinetic parameters for the adsorption process were determined through pseudo-first-order and pseudo-second-order kinetic models and intraparticle diffusion models. Equilibrium experiments and adsorption isotherms were analyzed using Langmuir and Freundlich adsorption isotherms. After reaching equilibrium, the activated carbon adsorbed quinoline in preference to pyridine: the equilibrium adsorptions from individual aqueous solutions (200 μL L^-1) of quinoline and pyridine were 166.907 mg g^-1 and 72.165 mg g^-1, respectively. Thermodynamic studies of quinoline adsorption were conducted at different temperatures and indicated that quinoline adsorption was an endothermic and spontaneous process. The column-adsorption of quinoline and pyridine was consistent with the Thomas model and the Yoon-Nelson model. The removal efficiency of quinoline reached more than 97% for a velocity of 6 mL min^-1 at the initial adsorption stage.

Lignin xanthate resin-bentonite clay composite as a highly effective and low-cost adsorbent for the removal of doxycycline hydrochloride antibiotic and mercury ions in water

Natural-occurring polymer intercalated inorganic clay composites have received increasing interests in water cleanup for the features of eco-friendliness, cost-effectiveness, and availability. Herein, a new lignin xanthate resin (LXR) intercalated bentonite clay composite (LXR-BT) for the adsorption of representative organic doxycycline hydrochloride (DCH) antibiotic and inorganic Hg(II) in water was created through a feasible process. Structural characterizations by X-ray diffraction (XRD), Fourier transform infrared (FTIR) spectroscopy, Thermo gravimetric analysis (TG), and scanning electron microscopy (SEM) confirmed LXR was successfully intercalated between the layers of bentonite clay. The adsorption performance of DCH/Hg(II) by LXR-BT was studied in detail with varied dosage, solution pH, contact time, and initial DCH/Hg(II) concentration. The results indicated that the adsorption capacities of DCH/Hg(II) on LXR-BT were much higher than that on bentonite, and the adsorption kinetics and isotherms followed the pseudo-second-order model and Langmuir model, respectively. X-ray photoelectron spectroscopy (XPS) analysis confirmed the adsorption mechanisms of DCH (or Hg(II)) was mainly due to π-π interaction and hydrogen bonding interaction of DCH (or the complexation of Hg(II)) with the functional groups in the LXR-BT. This study suggested the possibility of LXR-BT as a new cost-effective adsorbent for both organic and inorganic pollutants removal in water.

Laser-Induced Breakdown Spectroscopic (LIBS) Analysis of Trace Heavy Metals Enriched by Al2O3 Nanoparticles

We demonstrated a unique method for the detection of heavy metals, such as Ni, Cr, and Cd, at trace level in aqueous solutions by laser induced breakdown spectroscopy (LIBS) enriched by aluminum oxide (Al₂O₃) nanoparticles (NP) adsorption. Al₂O₃ NPs were used for the sample phase transformation and heavy metals pre-concentration because of its excellent adsorption capacity and sparse spectral lines. The influence of laser wavelength and laser irradiance on the signal intensity was investigated. With 45 mL solutions used for enrichment and adsorption, limits of detection obtained for Ni, Cr, and Cd were 9.61, 8.49, and 71.6 μg/L under 532 nm laser ablation, and 22.5, 20.4, and 83.8 μg/L under 1064 nm laser ablation, respectively. The relative standard deviations of all elements were about 12% or 13%. Moreover, Al₂O₃ NPs adsorption enrichment of target elements was verified and the detection sensitivity was improved by increasing the amount of sample solutions.

Adsorption of Cd(II) in water by mesoporous ceramic functional nanomaterials

Mesoporous ceramic functional nanomaterials (MCFN) is a self-assembled environmental adsorbent with a monolayer molecular which is widely used in the treatment of industrial wastewater and contaminated soil. This work aimed to study the relationship between the adsorption behaviour of Cd(II) by MCFN and contact time, initial concentration, MCFN dosage, pH, oscillation rate and temperature through a batch adsorption method. The adsorption kinetic and isotherm behaviours were well described by the pseudo-second-order and Langmuir models. The batch characterization technique revealed that MCFN had several oxygen-containing functional groups. Using Langmuir model, the maximum adsorption capacity of MCFN for Cd(II) was 97.09 mg g-1 at pH 6, 25°C, dosage of 0.2 g and contact time of 180 min. Thermodynamic study indicated that the present adsorption process was feasible, spontaneous and exothermic at the temperature range of 25-55°C. The results of this study provide an important enlightenment for Cd removal or preconcentration of porous ceramic nanomaterial adsorbents for environmental applications.

Sorption of Cu(II), Zn(II) and Pb(II) Ions in an Aqueous Solution on the PVC-Acetylacetone Composites

The possibility of removing Cu(II), Zn(II) and Pb(II) ions by sorption on new PVC-based composite materials with different contents of acetylacetone (acac) and porophor was investigated. Composites were characterized using a scanning electron microscope and by infrared spectral analysis (FTIR). Sorption tests were conducted at 20 °C. It has been shown that the equilibrium is established in about 4 h. The reduction in ion concentration in the solution depended on the content of both acac and porophor in the composite. The maximal reduction in ion concentration ranged from 8% to 91%, 10–85% and 6–50% for Cu(II), Zn(II) and Pb(II) ions, respectively, depending on the composite composition. The best results were obtained for the composite containing 30% w/w of acac and 10% of porophor. For this composite, the sorption capacity after 4 h sorption for Zn(II), Cu(II) and Pb(II) ions was 26.65, 25.40, and 49.68 mg/g, respectively. Kinetic data were best fitted with a pseudo–second-order equation.

Characteristics and performance of Cd, Ni, and Pb bio-adsorption using Callinectes sapidus biomass: real wastewater treatment

In the current study, the bio-adsorption potential of Callinectes sapidus biomass for control of cadmium, nickel, and lead from the aqueous stream was assessed. Spectrum analysis of FTIR, AFM, EDAX, mapping, SEM, TEM, and XRF was used to study the properties of the C. sapidus biomass. The XRF analysis revealed that C. sapidus bio-adsorbent has various effective metal oxides that can be useful to adsorb pollutants. The best model to describe the equilibrium data was Freundlich isotherm. The Langmuir bio-adsorption capacity was reported at 31.44 mg g^-1, 29.23 mg g^-1, and 29.15 mg g^-1 for lead, cadmium, and nickel ions, respectively. Pseudo-first-order and pseudo-second-order kinetic models were studied to test the kinetic behavior of the process. An intra-particle diffusion model was used to determine the effective mechanisms involved in the bio-adsorption. Based on t_1/2, it can be concluded that the equilibrium speed of the bio-adsorption process is high. The thermodynamic study showed that the metal bio-adsorption process using C. sapidus biomass is exothermic and spontaneous. The field applicability of the crab bio-adsorbent for eliminating concurrently several contaminants (metal ions, antibiotics, sulfate, nitrate, and ammonium) from an actual wastewater was successfully examined.

Study on the adsorption performance and competitive mechanism for heavy metal contaminants removal using novel multi-pore activated carbons derived from recyclable long-root Eichhornia crassipes

Long-root Eichhornia crassipes has shown great remediation capacity for eutrophication while the dispose of massive plants reaped is a pressing challenge for its large-scale application. In this study the waste plants were reclaimed and employed to prepare multi-pore activated carbons (MPAC) with high specific surface area through a simple gradient heating method. Owing to the large specific surface area and abundant multiple functional groups, the MPAC exhibited great adsorption performances for heavy metals with great adsorption capacities and rapid rate. Careful adsorption investigation indicated that the adsorption was mainly controlled by a charge transfer complex pattern. In addition, the adsorption impetuses were heterozygous involving electrostatic interaction, electron sharing or electronic-donor-acceptor interaction, etc. Moreover, the competitive adsorption reflected adsorption preference existed in the heavy metal removal using the MPAC as adsorbents due to the imparities in the adsorption affinity, thus resulting in the differences of the adsorption tolerance to exogenous influence.

Sustainable technologies for water purification from heavy metals: review and analysis

We review and analyze current water purification technologies in the context of sustainability, and we introduce the Ranking Efficiency Product (REP) index, to evaluate their efficiency and implementation in this broader perspective.

Voltammetry Determination of Pb(II), Cd(II), and Zn(II) at Bismuth Film Electrode Combined with 8-Hydroxyquinoline as a Complexing Agent

A novel method was developed for the simultaneous determination of Pb(II), Cd(II), and Zn(II) based on the cathodic stripping response at a bismuth film electrode associated with oxine as a chelating agent. The developed method provided a high and sharp electrochemical response compared with the method without oxine. A linear response of peak currents was observed for Pb(II), Cd(II), and Zn(II) concentration in the range from 2 ppb to 110 ppb. The detection limits of Pb(II), Cd(II), and Zn(II) were 0.45, 0.17, and 0.78 ppb, respectively. This method was successfully applied to the determination of Pb(II), Cd(II), and Zn(II) in lake-water and river-water samples. The metals were detected at the ultratrace level, showing the feasibility of the proposed method for environmental applications.

Cd2+ adsorption performance of tunnel-structured manganese oxides driven by electrochemically controlled redox

The heavy metal ion adsorption performance of birnessite (a layer-structured manganese oxide) can be enhanced by decreasing the Mn average oxidation state (Mn AOS) and dissolution-recrystallization during electrochemical redox reactions. However, the electrochemical adsorption processes of heavy metal ions by tunnel-structured manganese oxides are still enigmatic. Here, tunnel-structured manganese oxides including pyrolusite (2.3 Å × 2.3 Å tunnel), cryptomelane (4.6 Å × 4.6 Å tunnel) and todorokite (6.9 Å × 6.9 Å tunnel) were synthesized, and their electrochemical adsorptions for Cd²⁺ were performed through galvanostatic charge-discharge. The influence of both supporting ion species in the tunnel and tunnel size on the electrochemical adsorption performance was also studied. The adsorption capacity of tunnel-structured manganese oxides for Cd²⁺ was remarkably enhanced by electrochemical redox reactions. Relative to K⁺ in the tunnel of cryptomelane, the supporting ion H⁺ was more favorable to the electrochemical adsorption of Cd²⁺. With increasing initial pH and specific surface area, the electrochemical adsorption capacity of cryptomelane increased. The cryptomelane electrode could be regenerated by galvanostatic charge-discharge in Na₂SO₄ solution. Due to the differences in their tunnel size and supporting ion species, the tunnel-structured manganese oxides follow the order of cryptomelane (192.0 mg g^-1) > todorokite (44.8 mg g^-1) > pyrolusite (13.5 mg g^-1) in their electrochemical adsorption capacities for Cd²⁺.

Kinetics and Adsorption Studies of Mercury and Lead by Ceria Nanoparticles Entrapped in Tamarind Powder

In this study, novel adsorbent ceria nanoparticles (CeNPs) entrapped in tamarind powder (Tm@CeNPs) were efficiently utilized for the simultaneous adsorption of aqueous mercury [Hg(II)] and aqueous lead [Pb(II)]. Surface interactions between the adsorbent and heavy metal ions play an important role in the adsorption process, and the surface morphology can significantly improve the adsorption capacity of the adsorbent. The Langmuir adsorption capacity of Tm@CeNPs for Hg(II) and Pb(II) was found to be 200 and 142.85 mg/g, respectively. The surface area of utilized adsorbent was found to be very high, that is, 412 m2/g. The adsorption kinetics of Tm@CeNPs for both ions follow pseudo-second-order, and the adsorption process is also thermodynamically feasible. Column study favors multilayer adsorption of the heavy metal ion. The spectral analysis of the adsorbent revealed that hydroxyl, carboxylic, and ester groups, as well as CeNPs, are responsible for Hg(II) and Pb(II) adsorption. The cost-benefit analysis confirms the economic viability of the synthesized Tm@CeNPs composite for heavy metal removal. The adsorbent is best suited for Hg(II) adsorption as compared to Pb(II). This is a novel study on the utilization of tamarind leaf powder with CeNPs for heavy metal ion adsorption and its adsorption mechanism, which has not been reported to date.

Nitric acid-anionic surfactant modified activated carbon to enhance cadmium(II) removal from wastewater: preparation conditions and physicochemical properties

The authors used a nitric acid (HNO₃)-sodium dodecyl benzene sulfonate (SDBS) method to modify a lignite-based activated carbon. These modified carbons were appraised for their removal of Cd(II) from aqueous solutions. Response surface methodology was employed to optimize the preparation factors including nitric acid concentration C_N, temperature T and SDBS concentration C_S. Statistical analysis indicated that the interaction of C_N and C_S incurred the most effect on the maximum cadmium adsorption capacity (Q_m). The optimal Q_m appeared at C_N = 3.29 mol/L, T = 76 °C and C_S=30,700 mg/L. The optimal protocol achieved 44.21 mg/g Q_m for Cd(II) which was about 7 times larger than for this pristine lignite activated carbon (LAC) (6.78 mg/g). The physical-chemical properties of the modified activated carbons following each synthesis step were characterized relative to their surface area, oxygen functionality, and external surface charge. It was confirmed that the developed surface area, functional groups and negative charges were mainly responsible for the higher adsorption capacity for the LAC that have been more favorably tailored by this HNO₃-SDBS protocol.

Removal of Methylene Blue from Aqueous Solution by Bone Char

Bone char was prepared from bovine bone for the removal of methylene blue from aqueous solution. The effects of particle size, contact time, and adsorption temperature on the removal rate of methylene blue were investigated. It was found that bone char particle size had an insignificant effect. The equilibration time was found at approximately 80 min. The removal rate decreased with an increase in temperature. The intraparticle diffusion was the main rate-limiting step. The experimental data was analyzed by kinetic, isotherm, and thermodynamic equations. The results show that the pseudo-second-order kinetic model and Freundlich, Temkin, and Dubinin–Kaganer–Radushkevich isotherm models are true of the adsorption process. The spontaneous and exothermic ion-exchange adsorption process was certified by the negative values of free energy change and enthalpy change, and 13.29 kJ mol−1 of adsorption energy.

Functionalized layered double hydroxide with nitrogen and sulfur co-decorated carbondots for highly selective and efficient removal of soft Hg2+ and Ag+ ions

A facile composite was fabricated via direct assembly of nitrogen and sulfur co-decorated carbon dots with abundant oxygen-containing functional groups on the surface of the positively charged layered double hydroxide (N,S-CDs-LDH). The novel N,S-CDs-LDH demonstrates highly selective bindings (M-S) and an extremely efficient removal capacity for soft metal ions such as Ag⁺ and Hg²⁺ ions. N,S-CDs-LDH displayed a selectivity order of Ag⁺> Hg²⁺ >> Cu²⁺ >>> Pb²⁺ > Zn²⁺ > Cd²⁺ for their adsorption. The enormous capacities for Hg²⁺ (625.0 mg g^-1) and Ag⁺ (714.3 mg g^-1) and very high distribution coefficients (K_d) of 9.9 × 10⁶ mL g^-1 (C₀ = 20 mg L^-1) and 2.0 × 10⁷ mL g^-1 (C₀ = 20 mg L^-1) for Hg²⁺ and Ag⁺, respectively, place the N,S-CDs-LDH at the top of LDH based materials known for such removal. The adsorption kinetic curves for Hg²⁺ and Ag⁺ fitted well with the pseudo-second order model. For Hg²⁺ and Ag⁺, an exceptionally rapid capture with removal ∼100% within 80 min was observed (C_ions = 30 mg L^-1 and V/m ratio of 1000). The adsorption isotherms were well described using Langmuir isotherm. The N,S-CDs-LDH was successfully applied to highly efficient removal of Hg²⁺ and Ag⁺ from aqueous solutions.

Cadmium removal from simulated groundwater using alumina nanoparticles: behaviors and mechanisms

Cadmium (Cd), one of the most toxic contaminants in groundwater, can cause a severe threat to human health and ecological systems. In this study, alumina nanoparticles were synthesized and tested for high-efficiency Cd removal from simulated groundwater. Furthermore, the synthesized alumina nanoparticles were successfully modified using negatively charged glycerol, to alleviate the challenge of its low mobility in groundwater for the Cd removal. The maximum removal efficiency of both synthesized and glycerol-modified alumina nanoparticles were more than 99%. The sorption isotherm and kinetic data of both synthesized and glycerol-modified alumina nanoparticles were best fitted to the Freundlich model and the pseudo-second-order model, respectively, indicating that the sorption of Cd ions occurs on heterogeneous surfaces of both alumina nanoparticles via the chemisorption mechanism. X-ray photoelectron spectroscopy and energy dispersive X-ray analysis revealed the presence of Cd peak in both sorbents after contact with Cd. In addition, the FTIR analyses demonstrated that hydroxyl group participated in the sorption of Cd on both synthesized and glycerol-modified alumina nanoparticles, while other glycerol associated groups contributed to the removal of Cd ions by the glycerol-modified alumina nanoparticles. It was concluded that Cd removal by synthesized and glycerol-modified alumina nanoparticles were mainly due to ion exchange and electrostatic attraction, respectively. Desorption experiment suggested that both alumina nanoparticles are effective and practically significant sorbents to remediate Cd from contaminated groundwater. However, the stronger bond between Cd and glycerol-modified alumina, plus its potential of higher mobility due to the negative charge on the surface, warrant glycerol-modified alumina nanoparticles a better performance in remediating Cd contaminated groundwater than that of the synthesized alumina nanoparticles.

Preparation of rice straw-derived biochar for efficient cadmium removal by modification of oxygen-containing functional groups

In order to enhance the adsorption capacity of cadmium (Cd) ion from aqueous solution, the rice straw-derived biochar (BC800) was modified by a mixture of HNO₃ and H₂O₂ (MHH) with equal volume. Several elemental, chemical and structural characterization methods were used to determine the characteristics of biochars. Batch adsorption experiments were carried out concerning the influences of contact time, initial pH value, and initial concentration. The results indicated that the modified biochar (BCM) was more effective in removing Cd²⁺ from water than BC800. For 550mgL^-1 Cd²⁺ concentration solution, the adsorption capacity of 93.2mgg^-1 was observed for BCM, which was much higher than that of BC800 (69.3mgg^-1). The BCM had a significant increase of acidic functional groups with a rate of 101.6% and the component carboxyl, lacton and phenol groups increased by 124.1%, 29.3% and 111.3% respectively, while the specific surface area increased about 22.0%, compared with BC800. The pseudo-second-order model provided high correlation coefficients for BCM, speculating chemisorption of the Cd²⁺ onto biochars. Therefore, the rice straw-based biochar treated by MHH is considered to be an efficient adsorbent for Cd²⁺ removal from aqueous solution, especially for high concentrations of cadmium solution.

Removal of chromium (VI) from aqueous solution using vesicular basalt: A potential low cost wastewater treatment system

In this study, vesicular basalt volcanic rock was taken and its application for adsorption of chromium (VI) from aqueous solution was investigated. Different physical and chemical properties of the powdered rock was studied using Fourier transform infrared spectroscopy (FT-IR), Powder X-ray diffraction (XRD) and scanning electron microscopy (SEM). A series of batch experiments were carried out to study the effect of various experimental parameters (pH, ionic strength and contact time) on chromium (VI) adsorption. It was found that the removal efficiency of chromium (VI) decreased with increasing pH and ionic strength. The adsorption process was optimal at pH 2. The maximum adsorption capacity was 79.20 mg kg⁻¹ at an initial concentration of 5.0 mg L⁻¹ and adsorbent dosage of 50 g L⁻¹. In individual adsorption tests, Pseudo-second-order kinetic and Freundlich isotherm models could better describe chromium (VI) adsorption on the vesicular basalt. This study indicated that vesicular basalt, which is inexpensive, has the potential to remove chromium (VI) from polluted water.

Study of Isothermal, Kinetic, and Thermodynamic Parameters for Adsorption of Cadmium: An Overview of Linear and Nonlinear Approach and Error Analysis

Reports about presence and toxicity of Cd²⁺ in different chemical industrial effluents prompted the researchers to explore some economical, rapid, sensitive, and accurate methods for its determination and removal from aqueous systems. In continuation of series of investigations, adsorption of Cd²⁺ onto the stem of Saccharum arundinaceum is proposed in the present work. Optimization of parameters affecting sorption potential of Cd²⁺ including pH, contact time, temperature, sorbent dose, and concentration of sorbate was carried out to determine best suited conditions for maximum removal of sorbate. To understand the nature of sorption process, linear and nonlinear forms of five sorption isotherms including Freundlich and Langmuir models were employed. Feasibility and viability of sorption process were evaluated by calculating kinetics and thermodynamics of the process, while error analysis suggested best fitted sorption model on sorption data. Thermodynamic studies demonstrated exothermic nature of reaction, while kinetic studies suggested pseudo-second order of reaction.

Utilization of nano-cryptomelane for the removal of cobalt, cesium and lead ions from multicomponent system: Kinetic and equilibrium studies

Nano-cryptomelane was prepared and characterized using SEM with mapping, HRTEM, FT-IR spectra, thermal analysis and surface area. The diameter distribution of nano-cryptomelane was found to be 4-6 nm. Sorption performance of the prepared material was studied for the removal of Co²⁺, Cs⁺ and Pb²⁺ from a multi-system solution of equal molar ratio, 1:1:1. The sorption capacity of nano-cryptomelane was found to be 179.6, 442.6 and 716.9 mg/g for Co²⁺, Cs⁺ and Pb²⁺, respectively. The kinetic studies revealed that the sorption process obeys non-linear pseudo-second-order model and is controlled by an intra-particle diffusion mechanism. The equilibrium isotherm investigations outlined that the extended Langmuir isotherm model fits the data reasonably well and it is more applicable than Freundlich multicomponent sorption isotherm. The value of diffusion coefficient for the three metal ions is in the order 10^-17 m²/s which indicates the chemisorption nature of the process. The desorption percentage attains the maximum value (98.13%, 97.29 and 97.04 for lead, cesium and cobalt ions, respectively) using 0.7 mol/L of HNO₃. This revealed that nano-cryptomelane can be regenerated and reused for farther sorption of Pb²⁺, Cs⁺ and Co²⁺ from wastewater.

Entrapment of ball-milled biochar in Ca-alginate beads for the removal of aqueous Cd(II)

A novel adsorbent was synthesized through the entrapment of ball-milled biochar in Ca-alginate beads for the removal of aqueous Cd(II). Batch adsorption experiments were conducted to compare Cd(II) adsorption characteristics of ball-milled biochar (BMB), Ca-alginate (CA), and Ca-alginate entrapped ball-milled biochar (CA-BMB). All the tested adsorbents showed excellent sorption ability. The maximum Cd(II) adsorption capacity estimated with Langmuir isotherm modeling was 251.8 mg g^-1 for CA, 227.1 mg g^-1 for CA-BMB, and 40.0 mg g^-1 for BMB. The results demonstrate that entrapment of ball-milled biochar in Ca-alginate provides a low-cost and high-effective way for the removal of aqueous Cd(II).

Comparative performance of novel magnetic ion-imprinted adsorbents employed for Cd2+, Cu2+ and Ni2+ removal from aqueous solutions

Novel magnetic ion-imprinted polymer was prepared by use of SBA-15 as functional monomer, ethylene glycol dimethacrylate as cross linker, diphenylcarbazide as ligand, and Cd²⁺, Cu²⁺, and Ni²⁺ as the template of ion source. The adsorption capacity of the synthesized adsorbent was 111, 95, and 87 mg g^-1, respectively for cadmium, copper, and nickel. The selectivity of the adsorbents examined in the presence of different cations including Na⁺, K⁺, Ca²⁺, Mg²⁺, Zn²⁺, Co²⁺, Fe²⁺, Mn²⁺, Hg²⁺, and Pb²⁺ indicated that the synthesized ion-imprinted adsorbents were highly selective for the appropriate cations. Kinetic studies indicated that the adsorption process was very fast and the equilibrium was established within 5 min and followed the pseudo-second-order kinetic model. The used ion-imprinted adsorbent was readily regenerated by elution with 2 M HNO₃, and the regenerated adsorbent retained most of its initial capacity. The calculated thermodynamic parameters indicated that the adsorption process was spontaneous and endothermic.

Remediation of As(III) and Cd(II) co-contamination and its mechanism in aqueous systems by a novel calcium-based magnetic biochar

A novel calcium-based magnetic biochar (Ca-MBC), made by pyrolyzing the mixture of rice straw, iron oxide (Fe₃O₄) and calcium carbonate (CaCO₃), was developed in this study for remediation of co-pollution of arsenic and cadmium. Characteristics of the material showed that Fe₃O₄ and CaCO₃ were adhered on the surface of biochar. The experiments on the effects of pH, adsorption kinetics and isotherm revealed that the Ca-MBC had a great ability to adsorb arsenic and cadmium within 0.5 h for cadmium and 12 h for arsenic with a maximum adsorption capacity of 6.34 and 10.07 mg g^-1, respectively, and that the adsorption of both metals was pH-dependent from 2 to 12 with an optimal pH of pH 5. The mechanism of co-adsorption of Cd(II) and As(III) included both competitive and synergistic effects. The presence of As(III) enhanced Cd(II) adsorption by 3-16% while Cd(II) addition suppressed As(III) adsorption by 15-33%. The synergistic effects on As(III) and Cd(II) adsorption had resulted from the electrostatic interaction and the formation of type B ternary surface complexes. These new insights provide valuable information for the application of Ca-MBC as a potential adsorbent in treatment of water contaminated with As(III) and Cd(II).

DPF soot as an adsorbent for Cu(II), Cd(II), and Cr(VI) compared with commercial activated carbon

The use of carbon soot recovered from diesel particulate filters (DPF) has been investigated as a potential adsorbent for heavy metals including cadmium, chromium, and copper from wastewater. Results were compared with the adsorption performance of powder activated carbon (PAC). The uptake capacity of heavy metals for soot was found to be higher than PAC. And the thermodynamic study result for both soot and PAC indicated the adsorption procedures are exothermic. The adsorption studies were carried out for both single and binary systems. The data are best modeled by the monolayer model and Langmuir isotherm model for single systems. The adsorption mechanisms are more complex for binary systems. The kinetic studies indicated the adsorption happens rapidly within the first 1 h, and the results can be best modeled by pseudo-second-order model. The SEM-EDS analysis revealed the soot possesses higher porosity and surface area. Carboxylic and hydroxyl functional groups are the predominant surface functional group on both soot and PAC as revealed by FTIR and IEP values. The adsorption can be explained by both Van Der Waals force and electrostatic force. Graphical abstract ᅟ.

Removal of phenol by powdered activated carbon prepared from coal gasification tar residue

Coal gasification tar residue (CGTR) is a kind of environmentally hazardous byproduct generated in fixed-bed coal gasification process. The CGTR extracted by ethyl acetate was used to prepare powdered activated carbon (PAC), which is applied later for adsorption of phenol. The results showed that the PAC prepared under optimum conditions had enormous mesoporous structure, and the iodine number reached 2030.11 mg/g, with a specific surface area of 1981 m²/g and a total pore volume of 0.92 ml/g. Especially, without loading other substances, the PAC, having a strong magnetism, can be easily separated after it adsorbs phenol. The adsorption of phenol by PAC was studied as functions of contact time, temperature, PAC dosage, solution concentration and pH. The results showed a fast adsorption speed and a high adsorption capacity of PAC. The adsorption process was exothermic and conformed to the Freundlich models. The adsorption kinetics fitted better to the pseudo-second-order model. These results show that CGTR can be used as a potential adsorbent of phenols in wastewater.

Methanol-dispersed of ternary Fe3O4@γ-APS/graphene oxide-based nanohybrid for novel removal of benzotriazole from aqueous solution

A novel nanohybrid: Fe₃O₄ coated with γ-APS polymer deposited on graphene oxide (F@γ-A/G), to remove an emergent heterocyclic contaminant benzotriazole (BTA) from solution. F@γ-A/G was synthesized in methanol-dispersion via aminosilanization under ultra-sonication. We newly found that F@γ-A/G crystallite lattice has a 2D triangular-network intersection with angle of 60° in three types of d₃₁₁, d₂₂₀ and d₁₁₁ planes with different interplanar spacings. Textural characteristics did not affect BTA adsorption, which was desired at high temperature (40 °C), neutral solution (pH = 6) and controlled by endothermic process. Considering the maximum BTA adsorption capacity of 312.5 mg/g, which was much higher than previously reported adsorbents, the plausible mechanism was attributed to hydrophobic, electrostatic and π-π interaction. Effects of pH and temperature are significant on BTA adsorption to F@γ-A/G. Methanol was the best solvent for multiple cycle regeneration with only 2% loss of BTA removal efficiency even after five cycles of F@γ-A/G.

Efficiency Evaluation of Food Waste Materials for the Removal of Metals and Metalloids from Complex Multi-Element Solutions

Recent studies have shown the potential of food waste materials as low cost adsorbents for the removal of heavy metals and toxic elements from wastewater. However, the adsorption experiments have been performed in heterogeneous conditions, consequently it is difficult to compare the efficiency of the individual adsorbents. In this study, the adsorption capacities of 12 food waste materials were evaluated by comparing the adsorbents’ efficiency for the removal of 23 elements from complex multi-element solutions, maintaining homogeneous experimental conditions. The examined materials resulted to be extremely efficient for the adsorption of many elements from synthetic multi-element solutions as well as from a heavy metal wastewater. The 12 adsorbent surfaces were analyzed by Fourier transform infrared spectroscopy and showed different types and amounts of functional groups, which demonstrated to act as adsorption active sites for various elements. By multivariate statistical computations of the obtained data, the 12 food waste materials were grouped in five clusters characterized by different elements’ removal efficiency which resulted to be in correlation with the specific adsorbents’ chemical structures. Banana peel, watermelon peel and grape waste resulted the least selective and the most efficient food waste materials for the removal of most of the elements.

Towards magnetic responsive chalcogenides for efficient separation in water treatment: facile synthesis of magnetically layered chalcogenide Fe3O4/KMS-1 composite adsorbents and their zinc removal application in water

A novel easily separated magnetic chalcogenide based composite, Fe₃O₄/KMS-1, was successfully synthesized under vigorous stirring of a mixture in ethanol solution.

Adsorption Removal of 17β-Estradiol from Water by Rice Straw-Derived Biochar with Special Attention to Pyrolysis Temperature and Background Chemistry

Rice straw biochar that produced at three pyrolysis temperatures (400, 500 and 600 °C) were used to investigate the adsorption properties of 17β-estradiol (E2). The biochar samples were characterized by scanning electron microscopy (SEM), Fourier-transform infrared spectroscopy (FTIR), elemental analysis and BET surface area measurements. The influences of pyrolysis temperature, E2 concentration, pH, ionic strength, background electrolyte and humic acid were studied. Kinetic and isotherm results illustrated that the adsorption process could be well described by pseudo-second-order and Freundlich models. Experimental results showed that ionic strength had less influence on the adsorption of E2 by 500 and 600 °C rice straw biochar. Further, multivalent ions had positive impact on E2 removal than monovalent ions and the influence of the pyrolysis temperature was unremarkable when background electrolyte existed in solutions. The adsorption capacity of E2 decreased with the pH ranged from 3.0 to 12.0 and the humic acid concentration from 2 to 10 mg L-1. Electrostatic attractions and π-π interaction were involved in the adsorption mechanisms. Compared to low-temperature biochar, high-temperature biochar exhibited a better adsorption capacity for E2 in aqueous solution, indicated it had a greater potential for E2 pollution control.

Mercerized mesoporous date pit activated carbon-A novel adsorbent to sequester potentially toxic divalent heavy metals from water

A substantive approach converting waste date pits to mercerized mesoporous date pit activated carbon (DPAC) and utilizing it in the removal of Cd(II), Cu(II), Pb(II), and Zn(II) was reported. In general, rapid heavy metals adsorption kinetics for Co range: 25-100 mg/L was observed, accomplishing 77-97% adsorption within 15 min, finally, attaining equilibrium in 360 min. Linear and non-linear isotherm studies revealed Langmuir model applicability for Cd(II) and Pb(II) adsorption, while Freundlich model was fitted to Zn(II) and Cu(II) adsorption. Maximum monolayer adsorption capacities (qm) for Cd(II), Pb(II), Cu(II), and Zn(II) obtained by non-linear isotherm model at 298 K were 212.1, 133.5, 194.4, and 111 mg/g, respectively. Kinetics modeling parameters showed the applicability of pseudo-second-order model. The activation energy (Ea) magnitude revealed physical nature of adsorption. Maximum elution of Cu(II) (81.6%), Zn(II) (70.1%), Pb(II) (96%), and Cd(II) (78.2%) were observed with 0.1 M HCl. Thermogravimetric analysis of DPAC showed a total weight loss (in two-stages) of 28.3%. Infra-red spectral analysis showed the presence of carboxyl and hydroxyl groups over DPAC surface. The peaks at 820, 825, 845 and 885 cm-1 attributed to Zn-O, Pb-O, Cd-O, and Cu-O appeared on heavy metals saturated DPAC, confirmed their binding on DPAC during the adsorption.

Fe-MoS4: An Effective and Stable LDH-Based Adsorbent for Selective Removal of Heavy Metals

It has always been a serious challenge to design efficient, selective, and stable absorbents for heavy-metal removal. Herein, we design layered double hydroxide (LDH)-based Fe-MoS₄, a highly efficient adsorbent, for selective removal of heavy metals. We initially synthesized FeMgAl-LDH and then enriched its protective layers with MoS₄^2- anions as efficient binding sites for heavy metals. Various characterization tools, such as X-ray diffraction (XRD), Fourier transform infrared (FTIR) spectroscopy, Raman spectroscopy, scanning electron microscopy, energy-dispersive X-ray, X-ray photoelectron spectroscopy (XPS), CHN analysis, and inductively coupled plasma analysis, were applied to confirm structural and compositional changes during the synthesis of Fe-MoS₄ as final product. The prepared Fe-MoS₄ offered excellent attraction for heavy metals, such as Hg²⁺, Ag⁺, Pb²⁺, and Cu²⁺, and displayed selectivity in the order Hg²⁺ ∼ Ag⁺ > Pb²⁺ > Cu²⁺ > Cr⁶⁺ > As³⁺ > Ni²⁺ ∼ Zn²⁺ ∼ Co²⁺. The immense capacities of Hg²⁺, Ag⁺, and Pb²⁺ (583, 565, and 346 mg/g, respectively), high distribution coefficient (K_d ∼ 10⁷-10⁸), and fast kinetics place Fe-MoS₄ on the top of materials list known for removal of such metals. The sorption kinetics and isothermal studies conducted on Hg²⁺, Ag⁺, Pb²⁺, and Cu²⁺ suit well pseudo-second-order kinetics and Langmuir model, suggesting monolayer chemisorption mechanism through M-S linkages. XRD and FTIR studies suggested that adsorbed metals could result as coordinated complexes in LDH interlayer region. More interestingly, LDH structure offers protective space for MoS₄^2- anions to avoid oxidation under ambient environments, as confirmed by XPS studies. These features provide Fe-MoS₄ with enormous capacity, good reusability, and excellent selectivity even in the presence of huge concentration of common cations.

Interpretation of single and competitive adsorption of cadmium and zinc on activated carbon using monolayer and exclusive extended monolayer models

In this work, a modeling analysis based on experimental tests of cadmium/zinc adsorption, in both single-compound and binary systems, was carried out. All the experimental tests were conducted at constant pH (around neutrality) and temperature (20 °C). The experimental results showed that the zinc adsorption capacity was higher than that of cadmium and it does not depend on cadmium presence in binary system. Conversely, cadmium adsorption is affected by zinc presence. In order to provide good understanding of the adsorption process, two statistical physics models were proposed. A monolayer and exclusive extended monolayer models were applied to interpret the single-compound and binary adsorption isotherms of zinc and cadmium on activated carbon. Based on these models, the modeling analysis demonstrated that zinc is dominant in solution and more favorably adsorbed on activated carbon surface. For instance, in single-compound systems, the number of ions bound per each receptor site was n (Zn²⁺) = 2.12 > n (Cd²⁺) = 0.98. Thus, the receptor sites of activated carbon are more selective for Zn²⁺ than for Cd²⁺. Moreover, the determination of adsorption energy through the adopted models confirmed that zinc is more favored for adsorption in single-compound system (adsorption energies equal to 12.12 and 7.12 kJ/mol for Zn and Cd, respectively) and its adsorption energy does not depend on the cadmium presence in binary system. Finally, the adsorption energy values suggested that single-compound and binary adsorption of zinc and cadmium is a physisorption.

Kinetics, isotherm, and thermodynamic studies of methylene blue adsorption from water by Mytella falcata waste

This work evaluates the application of Mytella falcata shells, discarded in large quantities in the state of Alagoas, Brazil, as adsorbent for methylene blue dye (MB). It was investigated how the amount of adsorbent (M), the average particle diameter (G), and the agitation speed (A) affected the adsorption. Kinetic and equilibrium studies were conducted, and the pseudo-second-order equation adequately represented the kinetic data and isotherms following Liu's model (q _max = 8.81 mg g^-1 at 60 °C). The adsorption was spontaneous, favorable, and endothermic. Mytella falcata shell is a suitable adsorbent for MB and could potentially contribute to its removal from the environment.

Highly efficient simultaneous adsorption and biodegradation of a highly-concentrated anionic dye by a high-surface-area carbon-based biocomposite

Mesoporous high-surface-area activated carbon (MHSA-AC), which has a honeycomb structure, was produced from coconut shells by simultaneous chemical and physical activation and used for the rapid adsorption of an anionic dye, namely acid orange 10 (AO10), from water. Owing to its porosity and high Brunauer-Emmett-Teller surface area (2283.91 m²g^-1), MHSA-AC is a highly efficient adsorbent. It also has good biocompatibility and is a good immobilization carrier; the grooves on the MHSA-AC surface facilitate immobilization. Here, a new, highly efficient, and environmentally friendly simultaneous adsorption and biodegradation (SAB) process was developed. Highly concentrated AO10 (6000 mg L^-1, 20 mL) was removed with an efficiency of 100% (pH = 7, 35 °C) by SAB using cells immobilized on MHSA-AC (500 mg). The immobilized cells were used directly, without pretreatment; the SAB process is therefore simple and has good potential for application in the treatment of dyes in industrial wastewater.

Adsorption of Cd(II) and Pb(II) by in situ oxidized Fe3O4 membrane grafted on 316L porous stainless steel filter tube and its potential application for drinking water treatment

Removing heavy metal ions from aqueous solutions is one of the most challenging separations. In situ oxidized Fe₃O₄ membranes using 316L porous stainless steel filter tube have shown great potential for removing anion Cr(VI). Here we report the performances of the in situ oxidized Fe₃O₄ membranes for removing two toxic cations Cd(II) and Pb(II) commonly existing in water and their potential applications for drinking water purification. The membranes exhibited high removal efficiency: 97% at pH 9.0 for Cd(II) of 1.0 mg/L initial concentration and 100% at pH 5.0-6.0 for Pb(II) of 5.0 mg/L initial concentration. The maximum adsorption capabilities were estimated at 0.800 mg/g and 2.251 mg/g respectively for Cd(II) and Pb(II) at 318 K by the Langmuir model. Results of batch tests revealed the existence of electrostatic attraction and chemisorption. XRD and FT-IR analyses indicated that the chemisorption might be the insertion of Cd(II) and Pb(II) into the Fe₃O₄ crystal faces of 311 and 511 to form mononuclear or binuclear coordination with O atoms of Fe-O₆ groups. Competitive adsorption of Cd(II) and Pb(II) in binary solutions revealed a preferential adsorption for Pb(II). Na₂EDTA solution was used to regenerate the membranes, and the maximum desorption ratio was 90.29% and 99.75% respectively for Cd(II) and Pb(II). The membranes were able to efficiently lower Cd(II) and Pb(II) concentrations to meet the drinking water standards recommended by the World Health Organization and are promising for engineering applications aimed at drinking water purification.