Kinetic and thermodynamic investigations of surfactants adsorption from water by carbide-derived carbon

Removal of Organic Dyes, Polymers and Surfactants Using Carbonaceous Materials Derived from Walnut Shells

A series of new granular carbonaceous adsorbents was prepared via single-stage physical and chemical activation of walnut shells. Their suitability for removing various types of organic pollutants (represented by dyes, surfactants and water-soluble polymers) from the liquid phase was assessed. The activation of the precursor was carried out with CO2 and H3PO4 using conventional heating. Activated biocarbons were characterized in terms of chemical composition, acidic-basic nature of the surface, textural and electrokinetic properties as well as thermal stability. Depending on the type of activating agent used during the activation procedure, the obtained biocarbons differed in terms of specific surface area (from 401 to 1361 m2/g) and the type of porous structure produced (microporosity contribution in the range of 45-75%). Adsorption tests proved that the effectiveness of removing organic pollutants from the liquid phase depended to a large extent on the type of prepared adsorbent as well as the chemical nature and the molecular size of the adsorbate used. The chemically activated sample showed greater removal efficiency in relation to all tested pollutants. Its maximum adsorption capacity for methylene blue, poly(acrylic acid), poly(ethylene glycol) and Triton X-100 reached the levels of 247.1, 680.9, 38.5 and 61.8 mg/g, respectively.

Oxidized carbide-derived carbon as a novel filler for improved antifouling characteristics and permeate flux of hybrid polyethersulfone ultrafiltration membranes

Polyethersulfone (PES) is a widely used polymer for ultrafiltration (UF) membrane fabrication. In the current study, carbide-derived carbon (CDC) oxidized by acid treatment was utilized as a filler to fabricate a novel PES composites UF membranes. The successful oxidation of CDC was validated from presence of oxygen containing functional groups and improved oxygen content, from 5.08 at.% for CDC to 26.22 at.% for oxidized CDC (OCDC). The OCDC PES UF membranes were prepared at different loadings of OCDC between 0.5 and 3.0 wt%. The membrane porosity, pore size and surface free energy found to be improved while a noticeable reduction in water contact angle was observed with OCDC loading implying the improved hydrophilicity of PES membranes. Consequently, the pure water flux found to improve from 151.6 to 569.6 (L/(m². h)) for the 3.0 wt% modified OCDC membrane (M-3) which is 3.8 folds of the bare PES membrane. The antifouling characteristics were evaluated by humic acid (HA) filtration. The results revealed a significant enhancement in HA rejection with OCDC loading, the highest rejection was 96.8% for M-3 membrane. Additionally, the adsorption capacity of OCDC modified membranes found to decrease with OCDC loading indicating improved rejection of HA from the membrane surface. Moreover, M-3 demonstrated the maximum flux recovery ratio (FRR) of 92.3%. Reusability of the fabricated membranes was evaluated by deionized water/humic acid cycling filtration. The FRR was higher than 86.7% over three cycles of pure water/HA filtration for 140 min, indicated the excellent stability and reusability of the membranes. Overall, the OCDC was an effective filler for enhancing the PES UF membranes antifouling and permeability properties.

A Comparative Analysis of the Effect of Carbonaceous Nanoparticles on the Physicochemical Properties of Hybrid Polyethersulfone Ultrafiltration Membranes

Numerous studies have been previously reported on the use of nanoscale carbonaceous fillers, such as multi-walled carbon nanotubes (MWCNTs) and graphene oxide (GO), in polymeric ultrafiltration (UF) membranes; however, no insight has been clearly reported on which material provides the best enhancements in membrane performance. In this study, a comparative analysis was carried out to establish a comprehensible understanding of the physicochemical properties of hybrid polyethersulfone (PES) UF membranes incorporated with MWCNTs and GO nanoparticles at various concentrations. The hybrid membranes were prepared via the non-solvent-induced phase separation process and further characterized by field emission scanning electron microscopy and atomic force microscope (AFM). The AFM images showed homogeneous membrane surfaces with a reduction in the membrane surface roughness from 2.62 nm for bare PES to 2.39 nm for PES/MWCNTs and to 1.68 nm for PES/GO membranes due to improved hydrophilicity of the membranes. Physicochemical properties of the hybrid PES membranes were assessed, and the outcomes showed an enhancement in the porosity, pore size, water contact angle, and water permeability with respect to nanoparticle concentration. GO-incorporated PES membranes exhibited the highest porosity, pore size, and lowest contact angle as compared to PES/MWCNTs, indicating the homogeneous distribution of nanoparticles within the membrane structure. PES/MWCNTs (0.5 wt.%) and PES/GO (1.0 wt.%) hybrid membranes exhibited the highest water flux of 450.0 and 554.8 L m^-2 h^-1, respectively, at an applied operating pressure of 1 bar. The filtration and antifouling performance of the PES hybrid membranes were evaluated using 50 mg L^-1 of humic acid (HA) as a foulant at pH = 7. Compared to the bare PES membrane, the MWCNTs and GO-incorporated PES hybrid membranes exhibited enhanced permeability and HA removal. Moreover, PES/MWCNTs (0.5 wt.%) and PES/GO (1 wt.%) hybrid membranes reported HA rejection of 90.8% and 94.8%, respectively. The abundant oxygen-containing functional groups in GO-incorporated PES membranes resulted in more hydrophilic membranes, leading to enhanced permeability and fouling resistance. The antifouling properties and flux recovery ratio were improved by the addition of both nanoparticles. Given these findings, although both MWCNTs and GO nanoparticles are seen to notably improve the membrane performance, PES membranes with 1 wt.% GO loading provided the highest removal of natural organic matter, such as HA, under the same experimental conditions.

Carbide-derived carbon as an extraordinary material for the removal of chromium from an aqueous solution

In the present work, the adsorptive removal of chromium (Cr) from water by carbide-derived carbon (CDC) was investigated. The morphology and structure of the CDC were characterized by using FTIR, SEM, TEM, XRD, and N₂ adsorption-desorption measurements. The effect of adsorption parameters including contact time, initial Cr concentration, temperature, initial solution pH, and CDC dosage was examined on the removal of Cr ions. The kinetic analysis revealed that the experimental data on the removal of Cr ions on CDC is well correlated with the pseudo-second order kinetic model (with R² > 0.999), while the equilibrium data were fitted by the Redlich-Peterson isotherm model (with R² > 0.992). The Langmuir and Sips models were also in good compliance with the equilibrium data, indicating a monolayer coverage of Cr ions onto the CDC surface with some heterogeneous active adsorption sites. The CDC revealed a notable Langmuir adsorption capacity of 159.1 mg/g for Cr ions at pH 6 and room temperature. The thermodynamic analysis illustrated that the Cr ions elimination by CDC is a feasible adsorption process and endothermic in nature. After five adsorption/desorption cycles, less than 18% reduction in the adsorption capacity was obtained indicating the stability and reusability of the CDC. Moreover, the CDC demonstrated an excellent potential in removing the Cr ions from real brackish water. According to the adsorption data, both physical and chemical adsorption processes occurred, and the adsorption was mainly controlled by electrostatic interactions with a possible reduction of hexavalent Cr to trivalent Cr at acidic conditions.

Efficient Removal of Eriochrome Black T (EBT) Dye and Chromium (Cr) by Hydrotalcite-Derived Mg-Ca-Al Mixed Metal Oxide Composite

Eriochrome Black T (EBT) and chromium (Cr) are considered to be potential pollutants due to their toxicity and severe impact on the environment. In the current study, hydrotalcite-derived Mg-Ca-Al-LDO mixed metal oxide composite was prepared using a conventional co-precipitation method and explored in terms of the removal of Cr and EBT dye from aqueous solution in a batch mode adsorption process. The prepared Mg-Ca-Al-LDH, Mg-Ca-Al-LDO and spent Mg-Ca-Al-LDO adsorbents were characterized to propose the adsorption mechanism. Different adsorption parameters were examined, such as adsorbent dosage, initial concentration, pH, reaction temperature and contact time. The EBT adsorption kinetic results matched strongly with the pseudo-second-order model for both Cr (R2 = 0.991) and EBT (R2 = 0.999). The Langmuir isotherm model exhibited a maximum adsorption capacity of 65.5 mg/g and 150.3 mg/g for Cr and EBT, respectively. The structure and morphology results obtained after Cr and EBT dye adsorption reveal that the adsorption mechanism is associated with electrostatic interactions and surface complexation of Cr and EBT dye with Mg-Ca-Al-LDO surface functional groups. Moreover, more than 84% of the initial adsorption capacity of EBT and Cr can be achieved on the Mg-Ca-Al-LDO surface after five adsorption/desorption cycles. Finally, the Mg-Ca-Al-LDO mixed metal oxide composite can be potentially used as a cost-effective adsorbent for wastewater treatment processes.

Mg-Al Layered Double Hydroxide Doped Activated Carbon Composites for Phosphate Removal from Synthetic Water: Adsorption and Thermodynamics Studies

Increased phosphate concentration in water bodies has led to eutrophication, and its removal is an inevitable requirement of sustainable wastewater purification systems. In this study, MgAl layered doubled hydroxide (LDH) composites doped on the surface of activated carbon (AC/MgAl LDH) with various (Mg + Al) total metal loading (5 wt%, 10 wt%, and 15 wt%) were prepared by the co-precipitation method. The influence of (Mg + Al) total metal loading onto AC was examined to remove phosphate ions from aqueous solutions. The effect of adsorption parameters, including adsorbent dosage, initial solution pH, initial phosphate concentration, contact time, and experiment temperature, were investigated via batch adsorption experiments. The adsorption results demonstrated that the phosphate adsorption capacity significantly improved with increasing the (Mg + Al) metal loading on the surface of AC. The maximum Langmuir phosphate adsorption capacity was 337.2 mg phosphate per gram of AC/MgAl-3 LDH composite (15 wt% Mg + Al) composite at pH ~6.3, 22 °C, and 1 g/L of adsorbent. The kinetic data were best fitted with the pseudo-second order model. The initial solution pH notably influenced the phosphate removal by AC/MgAl-3 LDH composite with a maximum removal at pH 2.3. According to the spent adsorbent characterization results, the dominant mechanisms of phosphate removal by AC/MgAl-3 LDH were electrostatic interactions, ion exchange, and inner-sphere complexation. The phosphate adsorption capacity was gradually increased with increasing the experiment temperature, suggesting an endothermic adsorption process. Overall, the AC/MgAl LDH composites pave the way for an effective strategy for phosphate removal from aqueous solutions.