Use of Chrysosporium/carbon nanotubes for preconcentration of ultra-trace cadmium levels from various samples after extensive studies on its adsorption properties

ANN-assisted comprehensive screening of silica gel-alunite composite sorbent system for efficient adsorption of toxic nickel ions: Batch and continuous mode water treatment applications

Through batch and fixed-bed column operations, nickel ions were extracted from a contaminated aqueous media by adsorption onto silica gel-immobilized alunite (Sg@Aln). A three-layer backward-propagating network with an ideal pattern of 5-10-1 and 4-10-1 was used to train and validate an artificial neural network (ANN) model for process modeling and optimization in batch and continuous systems, respectively. For the test dataset, the model outputs of the model pointed out a satisfactory alignment between the anticipated and experimental response. The Sg@Aln dosage and contact time were recorded as the most relevant parameters in Ni2+ elimination. The Sg@Aln-metal interactions were also characterized using a variety of instrumental approaches. The maximum Ni2+ adsorption was achieved by utilizing 2 g/L of the adsorbent at a solution pH of 5.0 after 10 min of contact time, equating to 89.11%. The data corresponded well with the non-linear shape of the Langmuir isotherm (R2 = 0.99), and the computed maximal adsorption capacity was 96.01 mg/g (1.64 × 10-3 mol/g) at 25 °C. Kinetic analysis reveals that the adsorption process is consistent with the pseudo-second-order model, with R2 = 0.9998. Thermodynamic findings indicated endothermicity, spontaneity, and adsorption favorability. Sg@Aln could remove 41.23 mg/g and 33.20 mg/g of Ni2+ from actual wastewater in batch and continuous processes, respectively. While the Sg@Aln column's breakthrough curve is consistent with Chu's simplistic model, the breakthrough capacity was 69.35 mg/g. Overall, the results might open new possibilities for treating metal pollution in the aquatic environment.

Assessment of cerium adsorption potential of phosphoric acid activated biochar in aqueous system: Modelling and mechanistic insights

Cerium pollution in waterbodies by improper industrial waste disposal is a major concern due to its detrimental impacts on the environment. Therefore, treatment of cerium-contaminated water is inevitable. Hence, this study is focused on the remediation of cerium pollution using phosphoric acid-activated biochar (PPMB) as an adsorbent, synthesized upon pyrolytic activation of palmyra palm male flower-based pristine biochar (PMFB) with H3PO4 at 500 °C. The physico-chemical surface properties of PMFB and PPMB were evaluated through various microscopic and spectroscopic analyses. The key parameters such as biochar dosage, pH, temperature, contact time and initial cerium concentration were optimized as 0.5 g/L, 5.0, 303 K, 180 min and 50 mg/L respectively via batch adsorption. Pseudo-second order kinetic and Toth isotherm are the best-fitted models. The thermodynamic parameters including ΔG◦ (-30.4707 ± 0.7618 kJ/mol at 303 K), ΔH◦ (16.1499 ± 0.78 kJ/mol), and ΔS◦ (153.617 ± 3.8404 J/mol/K) conveying that cerium adsorption onto PPMB was spontaneous, endothermic, and highly disordered at PPMB-bulk adsorption medium interface. Precipitation, electrostatic attraction, and surface complexation are predicted to be the predominant mechanisms for the chosen PPMB-cerium adsorption system. Moreover, cerium phytotoxicity on Vigna radiata explains the real-time applicability and feasibility of cerium adsorption using PPMB. Thus, the key findings of this study specified that the higher adsorption capacity of PPMB (141.3484 ± 6.9856 mg/g) contributed by the incorporated phosphate groups, predominant mesoporosity, SSABET of 230.559 m2/g and anionic surface at a wider pH range (pH>3.08) make PPMB as efficient, economically feasible and environmentally friendly adsorbent for cerium adsorption in aqueous system.

Valorization of castor seed shell waste as lead adsorbent by treatment with hot phosphoric acid: Optimization and evaluation of adsorption properties

Lead is used in many industries such as refining, mining, battery manufacturing, smelting. Releases of lead from these industries is one of the major public health concerns due to widespread persistence in the environment and its resulting poisoning character. In this work, the castor seed shell (CSS) waste was exploited for preparing a beneficial bio-adsorbent for removal of Pb(II) ions from water. The raw CSS was modified with H3PO4 at different acid concentrations, impregnation ratios, activation times, and temperatures. An optimum adsorption capacity was observed for CSS modified with 2 M acid, 5 mL g-1 solid to liquid ratio, treated at 95 °C for 160 min. Exploiting acid modification, the SEM, XRD, and FTIR analyses show some alterations in functional groups and the surface morphology of the biomass. The impacts of physiochemical variables (initial lead ions concentration, pH, adsorbent dose and adsorption time) on the lead removal percentage were investigated, using response surface methodology (RSM). Maximum removal of 72.26% for raw CSS and 97.62% for modified CSS were obtained at an initial lead concentration (50 mg L-1), pH (5.7), adsorption time (123 min) and adsorbent dosage (1.1 g/100 mL). Isothermal and kinetics models were fitted to adsorption equilibrium data and kinetics data for the modified CSS and the adsorption system was evaluated thermodynamically and from the energy point of view. Isothermal scrutinization indicated the mono-layer nature of adsorption, and the kinetics experimental outcomes best fitted with the pseudo-second-order, implying that the interaction of lead ions and hot acid-treated CSS was the rate-controlling phenomenon of process. Overall, results illustrated that the hot acid-treated biomass-based adsorbent can be considered as an alternative bio-adsorbent for removing lead from water media.

Phosphate adsorption on dried alum sludge: Modeling and application to treatment of dairy effluents

This study evaluates Alum sludge from drinking water treatment plants for the efficient and cost-effective removal of phosphates from aqueous solutions. Extensive characterization and batch experiments have established that optimal phosphate removal was achieved with a sludge dosage of 20 g L-1 (at an initial phosphate concentration of 100 mg L-1), a pH of 5, a temperature of 23 °C, and a stirring speed of 200 rpm. These conditions significantly reduced phosphate levels, ensuring compliance with legal discharge limits. The Langmuir isotherm, pseudo-second-order kinetic and intraparticle diffusion models best described the adsorption process, highlighting the spontaneous and endothermic nature of the phenomenon. The sludge effectively reduced phosphate concentrations to acceptable levels when applied to dairy effluents. This study underscores the potential of Alum sludge as a viable solution for phosphate management in environmental cleanup efforts.

Selective adsorption of Cr(VI) by nitrogen-doped hydrothermal carbon in binary system

Selective adsorption of heavy metal ions from industrial effluent is important for healthy ecosystem development. However, the selective adsorption of heavy metal pollutants by biochar using lignin as raw material is still a challenge. In this paper, the lignin carbon material (N-BLC) was synthesized by a one-step hydrothermal carbonization method using paper black liquor (BL) as raw material and triethylene diamine (TEDA) as nitrogen source. N-BLC (2:1) showed excellent selectivity for Cr(VI) in the binary system, and the adsorption amounts of Cr(VI) in the binary system were all greater than 150 mg/g, but the adsorption amounts of Ca(II), Mg(II), and Zn(II) were only 19.3, 25.5, and 6.3 mg/g, respectively. The separation factor (SF) for Cr(VI) adsorption was as high as 120.0. Meanwhile, FTIR, elemental analysis and XPS proved that the surface of N-BLC (2:1) contained many N- and O- containing groups which were favorable for the removal of Cr(VI). The adsorption of N-BLC (2:1) followed the Langmuir model and its maximum theoretical adsorption amount was 618.4 mg/g. After 5th recycling, the adsorption amount of Cr(VI) by N-BLC (2:1) decreased about 15%, showing a good regeneration ability. Therefore, N-BLC (2:1) is a highly efficient, selective and reusable Cr(VI) adsorbent with wide application prospects.

PVA/PAA/DMTD electrospun nanofibrous membrane for the selective adsorption of Pb(II) ions in liquid foods

Lead (Pb(II)) contamination is common in liquid foods and can result from Pb(II) being present in the raw materials or during handling processes. However, due to the complexity of food matrices, there is limited data available concerning Pb(II) ion removal from food sources. This study focused on fabricating a PVA/PAA/DMTD electrospun nanofibrous membrane (ENFM) to efficiently and selectively remove Pb(II) ions from liquid foods. The PVA/PAA/DMTD ENFM had a maximum adsorption capacity of 138.3 mg/g for Pb(II) ions and demonstrated high selectivity toward the removal of Pb(II) ions. Negative values of the Gibbs free energy (ΔG°) showed that the spontaneous nature of the adsorption process was feasible at different temperatures. Moreover, it successfully removed Pb(II) ions from selected samples of commercially available drinks. Therefore, this adsorbent exhibits significant potential for removing Pb(II) ions from liquid food products, thereby reducing daily dietary exposure to Pb(II).

Studies on adsorption properties of magnetic composite prepared by one-pot method for Cd(II), Pb(II), Hg(II), and As(III): Mechanism and practical application in food

A one-pot synthesis afforded a magnetic, crosslinked polymer adsorbent (m-P6) with a variety of functional groups to realize simultaneous adsorption of Cd2+, Pb2+, Hg2+, and As3+. The material was characterized by TEM-EDS, XRD, FT-IR, VSM, and XPS. Kinetic and isothermal analyses suggested mainly chemisorption processes of heavy metal ions that form multiple layers on heterogeneous surfaces. Theoretical adsorption capacities calculated by a pseudo-2nd-order kinetic model and the Sips isothermal model were 282.88 mg/g for Cd2+, 326.18 mg/g for Pb2+, 117.85 mg/g for Hg2+, and 320.29 mg/g for As3+. m-P6 not only can efficiently adsorb divalent heavy metals (Cd2+, Pb2+, Hg2+), but also demonstrate a process of adsorption-driven catalytic oxidation by single-electron transfer (SET) from As3+ to As5+. In application, in addition to adsorption in water, m-P6 is capable of minimizing matrix interference, and extracting trace heavy metals in a complex environment (cereal) through easy operations for improving the detection accuracy, as well as it is potential for application in detection of trace heavy metals in foodstuffs. m-P6 can be readily regenerated and efficiently recycled for 5 cycles using eluent E12 and dilute acid.

Deep insights into kinetics, optimization and thermodynamic estimates of methylene blue adsorption from aqueous solution onto coffee husk (Coffee arabica) activated carbon

In the current study, an attempt was made to synthesize coffee husk (CH) activated carbon by chemical modification approach (sulphuric acid-activated CH (SACH) activated carbon) and was used as a valuable and economical sorbent for plausible remediation of Methylene blue (MB) dye. Batch mode trials were carried out by carefully varying the batch experimental variables: SACH activated carbon (SACH AC) dosage, pH, initial dye concentration, temperature, and contact time. The optimum equilibrium time for adsorption by SACH activated carbon was obtained as 60 min, and the maximum adsorption took place at 30 °C. Morphological and elemental composition, crystallinity behaviour, functional groups, and thermal stability were examined using SEM with EDX, XRD, FTIR, BET, TGA, and DTA and these tests showed successful production of activated carbon. The outcomes showed that chemical activation enhanced the number of pores and roughness which possibly maximized the adsorptive potential of coffee husk. The Box-Benken design (BBD) was used to optimize the MB dye adsorption studies and 99.48% MB dye removed at SACH AC dosage of 4.83 g/L at 30 °C for 60 min and pH 8.12, and the maximum adsorption was yielded for sulphuric acid-activated coffee husk carbon carbon with 88.1 mg/g maximum MB adsorption capacity. Langmuir- Freundlich model deliberately provided a better fit to the equilibrium data. The SACH AC-MB dye system kinetics showed a high goodness-of-fit with pseudo second order model, compared to other studied models. Change in Gibbs's free energy (ΔGo) of the system indicated spontaneity whereas low entropy value (ΔSo) suggested that the removal of MB dye on the SACH activated carbon was an enthalpy-driven process. The exothermic nature of the sorption cycle was affirmed by the negative enthalpy value (ΔHo). The adsorptive-desorptive studies reveal that SACH AC could be restored with the maximum adsorption efficiency being conserved after the fifth cycles. Overall, the outcomes revealed that sulphuric acid-activated coffee husk activated carbon (SACH AC) can be used as prompt alternative for low-cost sorbent for treating dye-laden synthetic wastewaters.

Efficient removal of Cr (VI) from aqueous solution using memory effect property of layered double hydroxide material

Treating wastewater containing pollutants with layered double hydroxide (LDH) material attracts excellent interest. LDH materials are known by the memory effect property, which leads to the reconstruction of the LDH structure after its calcination and rehydration. In this study, LDH material was prepared, calcined, and then rehydrated in an aqueous Cr(VI) solution. XRD, FTIR, and SEM-EDS analysis confirm the successful reconstruction of LDH-loading chromium on its surface and layered space. Response surface methodology (RSM) results showed that LDH mass, contact time, and chromium concentration are the main factors controlling the removal of Cr(VI). The heterogeneous sorption of chromium was described by fitting the equilibrium data to the Freundlich model. Analytical techniques, thermodynamic data, activation, and adsorption energies confirm that the removal process of Cr(VI) is endothermic, spontaneous, and physical nature. LDH exhibits good reusability performance with only a 7% reduction of initial adsorption capacity after five cycles of the calcination-rehydration process. These results show that the memory effect of LDH is helpful for the intercalation and the removal of emergent pollutants, especially for wastewater treatment.