Porous Carbon-based Materials Research Articles

Tailoring Porous N-Doped Carbon Nanospheres for 3D Bottom-Up Electrode Design: A Versatile Synthesis Toolbox for Particle Size Independent Pore Size Control.

The rational design of carbon-based electrode materials plays an important role in improving the electrochemical properties of both, energy storage and energy conversion electrodes and devices. For most applications, well-defined and easily processable porous carbon-based electrode materials with controlled particle morphology (ideally spherical), particle size, and intraparticle pore size are desired. Here, a hard-templating synthesis toolbox is reported for highly-monodisperse meso- and macroporous N-doped carbon nanospheres (MPNCs) as a versatile material platform for the 3D bottom-up design of porous electrodes. With this approach, it is possible to change the MPNC pore size without affecting the particle size. By changing the template size, the pore size is adjusted between 15 and 99nm while maintaining a particle size ≈300nm. MPNCs are further used in electrochemical double-layer capacitors (EDLCs) as model application to demonstrate pore size effects on the performance independently from particle size effects, resulting in increasing specific capacitances for decreasing pores sizes, which correlates well with the surface area of the MPNCs and mass transport phenomena in the electrode. In conclusion, the toolbox allows to control intraparticulate porosities while keeping interparticulate properties constant, essential parameters to enable a true bottom-up 3D electrode design.

Hybrid Particle Size Template Method for Controllable Synthesis of Nitrogen-Doped Multilevel Porous Carbon as High-Rate Zn-Ion Hybrid Supercapacitor Cathode Materials.

Achieving high rate performance without compromising energy density has always been a critical objective for zinc-ion hybrid supercapacitors (ZHSCs). The pore structure and surface properties of carbon cathode materials play a crucial role. We propose utilizing a hybrid particle size (20 and 40 nm) magnesium oxide templates to regulate the pore structure of nitrogen-doped porous carbon derived from the soybean isolate. The multilevel pore structure enhanced ion transport efficiency while also improving the utilization of micropores. Nitrogen doping and oxygen-containing functional groups enhanced the wettability of carbon materials with aqueous electrolytes and facilitated the chemisorption of Zn2+ on the carbon material surface. The nitrogen-doped multilevel porous carbon material (HT-NMPC-1/1) prepared with a 1 : 1 mass ratio of the two templates exhibited a specific capacity of 146.65 mAh g-1 at 0.2 A g-1. Moreover, the Swagelok cells assembled with HT-NMPC-1/1 and Zn foil achieved a high energy density of 121.5 W h kg-1, high power output of 166 W kg-1, and 93.09 % capacity retention after 8000 cycles at 2 A g-1. Therefore, HT-NMPC-1/1 is a highly promising candidate for ZHSCs cathode materials. Furthermore, the novel pore regulation strategy and straightforward preparation method offer valuable reference points for other porous carbon-based functional materials.

Fractal Strategy for Improving Characterization of N2 Adsorption–Desorption in Mesopores

The current studies primarily analyze the heterogeneity and complexity of mesopore structures based on low-temperature nitrogen (N2) adsorption curves and the Frenkel–Halsey–Hill (FHH) fractal model. However, these studies ignore the fact that the low-temperature N2 desorption curve can also reflect the desorption performance of the mesopore structure. In this research, novel fractal indicators for characterizing the adsorption–desorption performance of mesopores based on the fractal dimension from the N2 adsorption curves and N2 desorption curves are proposed. The novel fractal indicators I1 and I2 are applied to evaluate the adsorption–desorption performance of mesopores with pore size 2–5 nm and pore size 5–50 nm, respectively. The fractal indicator I1 shows an increasing trend with coalification, reflecting that the gas adsorption performance of 2–5 nm mesopores is enhanced with coalification. The fractal indicator I2 exhibits a trend of first increasing and then decreasing with coalification, indicating the gas desorption performance of mesopores with pore size 5–50 nm decreases first and then increases. The proposed indicators provide novel analytical parameters for further understanding the gas adsorption–desorption mechanism of porous coal-based or carbon-based materials.

TH-graphyne: a new porous bidimensional carbon allotrope.

Graphyne and two-dimensional porous carbon-based materials have garnered significant attention due to their interesting structural characteristics and essential properties for new technological applications. Within this scope, this work investigates the structural, thermal, electronic, optical, and mechanical properties of a novel two-dimensional allotrope that combines triangular (T) and hexagonal (H) rings, connected by acetylenic linkages (graphyne-like), thus named TH-graphyne (TH-GY). This study comprehensively characterizes the proposed system's behavior using density functional theory, ab initio molecular dynamics, and classical reactive molecular dynamics simulations. Our results confirm the structural stability of TH-GY. AIMD simulations demonstrate the material's thermal stability at elevated temperatures, while phonon dispersions indicate its dynamical stability. Electronic band structure calculations show that the system is metallic. The analysis of optical properties reveals intense activity in the visible and UV regions, with pronounced anisotropy. A machine learning interatomic potentials model was developed for TH-GY and used to determine the mechanical behavior of the system, which exhibits Young's modulus ranging from 263 to 356 GPa, highlighting its flexibility. Classical reactive MD simulations elucidate the fracture behavior of TH-GY, revealing distinct fracture patterns and mechanical anisotropy.

Enhanced passivation of lead and cadmium from contaminated farmland using biochar with tailored pore properties: Performance and mechanisms

The porous biochar (PBCPB) was prepared by one-step KHCO3-activated pyrolysis of corn stalks, which showed excellent passivation properties for Pb/Cd in soil (48.99 % or 46.74 %). Characterization results revealed that the PBCPB possessed a dense and network-like pore structure with a huge specific surface area of 1342.07 m2/g, which was conducive to the passivation of Pb/Cd. Batch experiments showed that PBCPB had excellent adsorption properties with the maximum absorption capacity of 117.61/48.24 mg/g. After 30 d of remediation, the bioavailable-Pb/Cd contents in 5.0 % of PBCPB treatment were reduced by 47.06 % and 58.42 %, respectively. The speciation transformation results uncovered that the contents of unstable Pb/Cd components gradually decreased with the increase of PBCPB dosages, ultimately transforming into stable residual components. In addition, the PBCPB could effectively increase the contents of soil available nutrients and enhance functional enzyme activities, which contributed to promoting the growth of cucumber seedlings. Meanwhile, PBCPB strongly alleviated the oxidative damage of Pb/Cd to cucumber seedlings by significantly reducing the Pb/Cd accumulation and antioxidant oxidase activity of cucumber seedlings. Furthermore, precipitation, complexation, as well as cation-π interaction were the primary passivation mechanisms of PBCPB for Pb/Cd. Overall, the study provided a reasonable design of porous carbon-based materials for the remediation of Pb/Cd-contaminated soil.

Nanoconfined Supercooled Water in Hydrated Two-Dimensional Polyaniline for Sub-Zero Solid-State Zinc-Ion Hybrid Capacitor.

Solid-state electrochemical energy systems have attracted numerous attentions for their excellent performance, high safety, and low cost. Recently, ice of aqueous electrolytes is reported as a new kind solid-state electrolyte for low-temperature solid-state devices. However, the lack of kinetically favorable electrodes hampers the performance of this new class of icy electrolyte-based solid-state devices at sub-zero temperatures. In this work, a hydrated layered polyaniline cathode active material (h-LPANi) with nanoconfined supercooled water by metatungstate clusters is utilized to improve the performance of sub-zero solid-state zinc ion hybrid capacitors (ZIHCs). The interlayer confined hydrated network of h-LPANi improves kinetics, surpassing pristine polyaniline and conventional porous carbon-based active materials. At -15°C, the solid-state iced ZIHCs with h-LPANi cathode demonstrate an areal energy density of 580.0µWhcm-2 at 1.1mWcm-2 and 155.7µWhcm-2 at 43.3mWcm-2, surpassing other low-temperature solid-state ZIHCs with conventional cathodes.

Investigation of mechanical behavior of porous carbon-based matrix by molecular dynamics simulation: Effects of Si doping

Understanding the mechanical properties of porous carbon-based materials can lead to advancements in various applications, including energy storage, filtration, and lightweight structural components. Also, investigating how silicon doping affects these materials can help optimize their mechanical properties, potentially improving strength, durability, and other performance metrics. This research investigated the effects of atomic doping (Si particle up to 10 %) on the mechanical properties of the porous carbon matrix using molecular dynamics methods. Young's modulus, ultimate strength, radial distribution function, interaction energy, mean square displacement and potential energy of designed samples were reported. MD outputs predict the Si doping process improved the mechanical performance of porous structures. Numerically, Young's modulus of the C-based porous matrix increased from 234.33 GPa to 363.82 GPa by 5 % Si inserted into a pristine porous sample. Also, the ultimate strength increases from 48.54 to 115.93 GPa with increasing Si doping from 1 % to 5 %. Silicon doping enhances the bonding strength and reduces defects in the carbon matrix, leading to improved stiffness and load-bearing capacity. This results in significant increases in mechanical performance. However, excess Si may disrupt the optimal bonding network, leading to weaker connections within the matrix. Also, considering the negative value of potential energy in different doping percentages, it can be concluded that the amount of doping added up to 10 % does not disturb the initial structure and stability of the system, and the structure still has structural stability. So, we expected our introduced atomic samples to be used in actual applications.

N/Se co-doped porous carbon catalyst derived from a deep eutectic solvent and chitosan as green precursors: Investigation of catalytic activity for metal-free oxidation of alcohols

Heteroatom-doped porous carbon-based materials with high surface area compared to their metal-based homologs are considered environmentally friendly and ideal catalysts for organic reactions. In this paper, a new method for the convenient fabrication, cost-effective, and high efficiency of nitrogen/selenium co-doped porous carbon-based catalysis (marked as N/SePC-T) was designed. The N/SePC-T catalysts were created from the direct pyrolysis of a eutectic solvent containing choline chloride/urea as the nitrogen-rich carbon source, selenium dioxide as a source of heteroatom and chitosan as a secondary carbon source in different temperatures (T). The efficacy of the carbonization temperature on the pore structure, morphology, and catalytic activity of the N/SePC-T materials was investigated and displayed, the N/SePC-900 (having a surface area of 562.01 m2/g and total pore volume of 0.2351 cm3 g−1) has the best performance. The morphology, structure, and physicochemical properties of N/SePC-900 were characterized using various analyses including XRD, TEM, TGA, FE-SEM, EDX, FT-IR, XPS, and Raman. The optimized N/SePC-900 catalyst indicated excellent catalytic performance in the oxidation of benzylalcohols to corresponding aldehydes in very mild conditions.

In Situ Self-Assembly of Nitrogen-Doped 3D Flower-like Hierarchical Porous Carbon and Its Application for Supercapacitors.

The hierarchical porous carbon-based materials derived from biomass are beneficial for the enhancement of electrochemical performances in supercapacitors. Herein, we report the fabrication of nitrogen-doped 3D flower-like hierarchical porous carbon (NPC) assembled by nanosheets using a mixture of urea, ZnCl2, and starch via a low-temperature hydrothermal reaction and high-temperature carbonization process. As a consequence, the optimized mass ratio for the mixture is 2:2:2 and the temperature is 700 °C. The NPC structures are capable of electron transport and ion diffusion owing to their high specific surface area (1498.4 m2 g-1) and rich heteroatoms. Thereby, the resultant NPC electrodes display excellent capacitive performance, with a high specific capacitance of 249.7 F g-1 at 1.0 A g-1 and good cycling stability. Remarkably, this implies a superior energy density of 42.98 Wh kg-1 with a power density of 7500 W kg-1 in organic electrolyte for the symmetrical supercapacitor. This result verifies the good performance of as-synthesized carbon materials in capacitive energy storage applications, which is inseparable from the hierarchical porous features of the materials.

Dipole-induced hydrogen bonds enhanced P/O co-doped Lyocell-based porous carbon fiber cloth for hydrogen storage under ambient pressure

Currently, the hydrogen storage application of carbon-based adsorbent materials is mostly implemented under the pressure conditions of 30–300 bar, while there is few targeted studies conducted on the unsaturated adsorption under ambient pressure conditions. Therefore, based on industrialized Lyocell biopolymer fiber precursors and the enhancement effects of dipole-induced hydrogen bonds (DIHB), this work presents a facile construction strategy for P/O co-doped Lyocell-based porous carbon fiber cloth (Ly-ACF-F40). By the technical route of thermal stabilization---sonication assisted phosphoric acid activation---hydrogen bonds introduced by interfacial fluorination, the constructed Ly-ACF-F40 acquires a high specific surface area (1870 m2/g) and total pore volume (1.277 cm3/g), and an excellent hydrogen storage capacity of 3.22 wt% under ambient pressure conditions (77 K, 1 bar). The study directly demonstrated in the experiment that dipole induced hydrogen bonding H(I)-H(II)···F can effectively enhance the atmospheric hydrogen storage density on the basis of other eliminating influencing factors of specific surface area. The simple construction strategy of porous carbon-based materials can provide reference for the research of unsaturated adsorption hydrogen storage materials under ambient pressure conditions, also assist in the application and promotion of low-cost solid hydrogen storage materials.

Modified biochar activated by traditional Chinese medicine extract and its removal of tetracycline

Traditional Chinese medicine (TCM) has been widely used during the outbreak of Covid-19 in the past few years, causing waste of resources and environmental pollution. This paper will convert TCM into porous carbon-based materials through pyrolysis technology, and then combine it with TCM extract activator to synthesize a new type of adsorbent. The two main ingredients of Chinese patent medicine “Lianhua Qingwen Capsules”, Honeysuckle and Forsythia suspensa, will be used as raw materials. After the two herbs are crushed, the leachate is extracted, and the remaining residue is collected. The dried residue is activated and carbonized at high temperature to generate biochar. Further, the biochar will be soaked in TCM extraction liquid to load active ingredients. The adsorption mechanism of tetracycline (TC) by TCM biochar was explored based on the adsorption kinetics and adsorption isotherm fitting results. The microstructure, surface functional groups and crystal structure of TCM biochar will reveal the material properties of the adsorbent. The results show that compared with biochar without extract activation, the adsorption effect of combined biochar (BC-C) with the proportion of “Lianhua Qingwen Capsules” is greatly improved. BC-C has richer surface functional groups through TCM extract loading, which provides superior TC adsorption capacity (36.92 mg/g). The adsorption process of TC by TCM biochar follows the pseudo-second-order adsorption kinetic model and Freundlich adsorption isotherm model. The adsorption mechanism mainly involves pore filling, hydrogen bonding, electrostatic interaction and π-π interaction.

Disclosing the intrinsic nature of efficient removal of antibiotics in N/S dual-doped porous carbon-based materials: The manipulation of internal electric field

N/S co-doping has emerged as a prevailing strategy for carbon-based adsorbents to facilitate the antibiotic removal efficiency. Nevertheless, the underlying interplay among N, S, and their adjacent vacancy defects remains overlooked. Herein, we present a novel in situ strategy for fabricating pyridinic-N dominated and S dual-doped porous carbon adsorbent with rich vacancy defects (VNSC). The experimental results revealed that N (acting as the electron donor) and S (acting as the electron acceptor) form an internal electric field (IEF), with a stronger IEF generated between pyridinic-N and S, while their adjacent vacancy defects activate carbon π electrons, thus enhancing the charge transfer of the IEF. Density functional theory (DFT) calculations further demonstrated that the rich charge transfer in the IEF facilitated the π-π electron donor-acceptor (EDA) interaction between VNSC and tetracycline (TC) as well as norfloxacin (NOR), and thus is the key to adsorption performance of VNSC. Consequently, VNSC exhibited high adsorption capacities toward TC (573.1 mg g−1) and NOR (517.0 mg g−1), and its potential for environmental applications was demonstrated by interference, environmentally relevant concentrations, fixed-bed column, and regeneration tests. This work discloses the natures of adsorption capacity for N/S dual-doped carbon-based materials for antibiotics.

Adsorption site identification and regulation to guide design of N-doped porous carbon-based materials for efficient and selective removal of bisphenol a

Currently, identification and regulation of adsorption sites of carbon-based materials remain a major challenge. In this study, given the properties of the target contaminant, bisphenol A (BPA), we report a novel method for preparing ultra edge N-doped hierarchically porous carbon-based material with rich vacancy defects (HENDC) via a direct pyrolysis of simultaneous EDTA-4Na and g-C3N4. Interestingly, g-C3N4 kills three birds with one stone, including pore-forming agent, nitrogen configuration regulator, and structural defect former. As such, compared with that of MNDC, which was direct pyrolysis of EDTA-4Na (462.5 mg g−1 for BPA and 551.2 mg g−1 for bisphenol S (BPS)), the adsorption capacity of HENDC for BPA was 870.1 mg g−1, which exceeded that for BPS (793.3 mg g−1). Also, HENDC shortened the adsorption process to 10 min for BPA compared with MNDC (30 min) and displayed a promising environmental application potential. Based on experiments and theoretical calculations, the high adsorption performance of HENDC for BPA originated from edge nitrogen doping, defect inducing, and hierarchically porous structures. Specifically, Lewis acid-base interactions of varying strength occurred between both pyridinic-N (stronger) and pyrrolic-N (weaker) with BPA. A strong π-π EDA interaction between pyridinic-N and BPA, which was further facilitated by vacancy defects in adjacent edge nitrogen. The hydrophobic effect promoted the interaction between pyrrolic-N and BPA. This work offers deep insights into effective and selective removal of BPA, suggesting new strategies for exploring cost-effective carbon-based adsorbents.

Enhanced adsorption of perfluorooctanesulfonic acid (PFOS) in fluorine doped mesoporous carbon: Experiment and simulation

Per- and polyfluoroalkyl substances (PFAS) are new types of emerging pollutants that have contaminated major water sources of developed and developing countries. Porous carbon-based materials are considered as universal adsorbents of all types of PFAS molecules. We have synthesized bimodal mesoporous carbon with fluorine and nitrogen functionalities for better removal for perfluorooctanesulfonic acid (PFOS) as the model PFAS molecule. All the mesoporous carbons with fluorine functionalities demonstrated the better adsorption of PFOS, and the adsorption amounts were better than that of commercial activated carbon. Kinetics measurements confirmed a remarkable improvement in saturation time of mesoporous carbon (1 h) compared to that commercial carbon (50 h). This mesoporous carbon also successfully removed PFAS from different complex matrices, including influent and effluent wastewater, and landfill leachate. Molecular simulation results revealed that presence of fluorine on the carbon surface increases the hydrophobicity of the carbon surface and Lennard-Jones (LJ) potential of the PFOS with the carbon leading to the enhanced adsorption of PFOS. Simulation study confirms that the presence of fluorine provides a good interaction of PFOS with the carbon surface. Molecular simulation also revealed that, despite nitrogen functionalities decrease hydrophobicity of the carbon surface, it may increase the LJ potential of PFOS with carbon surface leading to enhanced PFOS adsorption. However, as the improvement in LJ potential may be caused by much higher nitrogen content than what is present in the current system, it can be confirmed that the elevated PFOS adsorption is primarily contributed by the fluorine functionalities.

Electrochemical properties of porous carbon derived from coal gasification fine ash via low-temperature alkaline fusion and KOH activation

Coal gasification fine ash (a carbon-based solid waste, CGFA) is regarded as the ideal precursors for constructing carbon-based porous materials due to their low cost, high yield, high carbon content, and abundant pore structure. This study employed CGFA as the raw material and prepared porous carbon samples with a high specific surface area (SBET) of 2167.5 m2/g and a high mesoporous ratio of 80.1 % (by volume) using an low-temperature alkaline fusion-KOH activation method. The sample exhibited ideal double-layer capacitance behavior with a mass-specific capacitance of 219.7 F/g (at 1 A/g) and a capacitance retention rate of 82.6 % (at 1 A/g–20 A/g). The energy density of the assembled symmetrical supercapacitor was 13.4 Wh/kg (corresponding to a power density of 475 W/kg), and the capacitance retention rate was 97.9 % after 15,000 cycles. In summary, this work prepared high-performance porous carbon for supercapacitors from widely existing industrial waste CGFA, which provides a feasible strategy for the application of CGFA derived porous carbon in energy storage materials.

Optimizing the application of high-performance supercapacitors: Utilizing 3D honeycomb mesoporous carbons derived from hybrid biomass

Biomass garbage convert into highly efficient porous carbon-based electrode materials for supercapacitors is of great significance to the current energy-friendly society. Herein, an efficient electrode material of three-dimensional honeycomb porous carbons is developed for supercapacitor by employing sunflower plate and rice husk as a precursor. Particularly, SiO2-rich rice husk plays a crucial role in the formation of porous structure and three-dimensional morphology. Benefiting from the high surface area and more defective carbon nano-framework, high contents of nitrogen and oxygen dopants, abundant porosity, the resultant optimal RSC-1-1 exhibits a specific capacitance of 448 F/g at 0.5 A/g in 6 M KOH. Furthermore, the capacitive performance of RSC-1-1 in acidic and neutral media are also analysed systematically. In addition, the energy densities of RSC-1-1 assembled supercapacitors 6 M KOH, 1 M Na2SO4 and PVA/KOH gels are 12.15 Wh/kg, 35.55 Wh/kg, and 29.06 Wh/kg, respectively. This study demonstrates the great potential of twin substance derived electrode materials in constructing high performance supercapacitor.

Facile fabrication of biomass chitosan-derived magnetic carbon aerogels as multifunctional and high-efficiency electromagnetic wave absorption materials

Biomass chitosan-derived porous carbon-based materials take the advantage of light weight, adjustable intrinsic conductivity, and environmental friendliness, attracting more attention in the field of electromagnetic compatibility. However, exploring a facile fabrication method to achieve rational structure design and electrical-magnetic coupling for electromagnetic absorption performance enhancement still remains challenging. Here, a unique honeycomb-like porous cobalt/carbon aerogel is fabricated through the directional freezing-drying and carbonization process, and abundant and even-distributed cobalt particles in-situ grow on the carbon skeletons. The aerogel exhibits an impressive electromagnetic wave absorption performance of a −75.8-dB absorption intensity and a −256.9-dB mm−1 specific reflection loss at a low filling content (10%), as well as an 8.53-GHz effective absorption bandwidth. Besides, the aerogel also demonstrates classy radar stealth and thermal insulation performance. The eco-friendly, easily fabricated, and high-performance cobalt/carbon aerogel suggests broad application prospects for electromagnetic compatibility and protection, thermal management, and multifarious electron devices.

Design and preparation of hierarchical porous carbon-based materials with bionic “ant nest” structure for high performance asymmetric supercapacitors

Rational design of electrodes to broaden the working potential window is an attractive approach to improve the energy density of asymmetric supercapacitors. Herein, a simple non-solvent-induced phase separation method was used to construct a bionic "ant nest" three-dimensional hierarchical porous carbon (HPC) without any template, realizing a three-dimensional interlaced interconnection network structure similar to that of a natural ant nest, which adsorbs more ions through a larger accessible area and facilitates the bi-continuous transport of ions and electrons. Further, the aqueous asymmetric supercapacitor assembled with MnO2-modified HPC (HPC/MnO2) as the positive electrode and nitrogen-doped HPC (NHPC) as the negative electrode has an energy density as high as 21 Wh kg−1 at a power density of 410 W kg−1, and as high as 17 Wh kg−1 even at a power density of 13 kW kg−1. The device exhibits an excellent electrochemical performance over a potential window of 0–1.6 V.

Carbon-Based Porous Materials for Energy Storage Applications

Carbon-based materials have many applications in energy storage devices, including batteries and electrochemical capacitors. These materials are sourced from a wide range of raw materials. This project focuses on finding and evaluating electrochemical applications for porous carbon-based materials made from domestic sources. This presentation will focus on our efforts to develop and characterize these porous (at different scales) carbon materials, and on several emerging energy storage applications being investigated at Ohio University. Comparisons with other porous energy storage materials will be made in consideration of process economics and performance.

Novel carbon-based composites enriched with Fe and Mn as effective and eco-friendly adsorbents of heavy metals in multicomponent solutions

With increasing demand for adsorbents highly effective in pollutant removal, carbon-based porous materials are becoming more and more popular. In this work, a new approach to the synthesis of such solids using an environmentally friendly, two-step preparation method is presented. A series of hybrid porous silica-containing carbon composites was synthesized, namely: metal free (C/SiO2), enriched with manganese (C/Mn/SiO2), as well as iron (C/Fe/SiO2). The effect of additives on the structure and morphology of the composites was evaluated using X-ray photoelectron spectroscopy (XPS), nitrogen adsorption/desorption and scanning electron microscope (SEM). The as-synthesized carbons were used as effective adsorbents for the simultaneous removal of heavy metals, including lead (Pb(II)) and zinc (Zn(II)) ions. In particular, it was determined that C/Mn/SiO2 sample demonstrated the highest adsorption capacity towards Pb(II) and Zn(II) ions. It was equal to 211.60 mg/g for Pb(II) and 74.95 mg/g for Zn(II). Zeta potential and surface charge density of the solids, with and without metals, were investigated to determine electrical double layer structure, whereas stability studies and aggregate size measurements were performed to estimate solid aggregation under selected conditions. It was established that solids with adsorbed metals formed suspensions with lower stability than those without ions. This, in turn, facilitates their separation from aqueous solutions.