Adsorption Thermodynamic Parameters Research Articles

Adsorption of NMST from acetic acid on coconut activated carbon: Kinetics, isotherms and thermodynamics

ABSTRACT Exploration has been made into 2-nitro-4-methylsulfonyltoluene (NMST) adsorption on coconut activated carbon from acetic acid. The results demonstrate that the adsorption of NMST on activated carbon augments with its concentration in acetic acid. NMST adsorption on activated carbon is also improved with temperature. Though NMST adsorption on per gram of carbon will decrease with carbon dosage, more NMST will be adsorbed. The kinetic study depicts that NMST adsorption on activated carbon is in good agreement with the pseudo-second-order kinetic equation. Both of the Langmuir and Freundlich equilibrium isotherm models are well fit for the experimental results, with R2 = 0.9994 and 0.9979, respectively. The adsorption thermodynamic parameters (ΔH, ΔG, ΔS) calculated with Van’t Hoff equations indicate that NMST adsorption on carbon is spontaneous and endothermic.

Diclofenac sodium adsorption in aqueous media by activated carbon obtained from einkorn (Triticum monococcum L.) husk

AbstractThe uncontrolled release of waste diclofenac with low biodegradability is considered to be a potential threat for the environment and creatures. To find effective solution for this issue, this study reports the adsorption performance of diclofenac sodium salt (DCF) by using activated carbon (EHAC) obtained from einkorn (Triticum monococcum L.) husk in aqueous solution under various circumstances. It was found that DCF adsorption on EHAC was highly solution pH dependent, and DCF adsorption by EHAC decreased with increasing adsorption temperature. Equilibrium data showed that fitted isotherm model with the experiment results of DCF adsorption on EHAC followed the order of Langmuir > Temkin > Freundlich > Dubinin-Radushkevich. Adsorption capacity of EHAC for DCF adsorption in aqueous solution was calculated to be 147.06 mg/g at 25 °C. The adsorption kinetic of DCF adsorption on EHAC was determined to obey the pseudo-second-order kinetic model. By utilizing FTIR and pH data obtained from DCF adsorption on EHAC, DCF adsorption mechanisms with some interactions such as π-π stacking, electrostatic interactions, and hydrogen bonding were suggested at diverse pH values. Additionally, intraparticle diffusion model was applied to kinetic results to further recognize the kinetic mechanism of DCF adsorption on EHAC. Furthermore, thermodynamic parameters for DCF adsorption on EHAC were calculated and evaluated, in which DCF adsorption process by EHAC was determined to be exothermic, spontaneous, and feasible.

Ruthenium sorption onto Fe3O4@MnO2: equilibrium, kinetic and thermodynamic study

Core–shell magnetic adsorbent Fe3O4@MnO2 was prepared and successfully used to ruthenium adsorption from aqueous solutions with 98% efficiency. The adsorption isotherms, kinetic and thermodynamic parameters for Ru(III) sorption onto Fe3O4@MnO2 were studied via a batch adsorption system. Adsorption isotherm models such as: Langmuir, Freundlich and Temkin were tested while the kinetic adsorption data were analyzed by pseudo-first order, pseudo-second order, and Weber-Morris models. It has been found that the adsorption process of Ru(III) onto Fe3O4@MnO2 can be describe by a Freundlich model whereas mechanism of sorption is presented better by kinetic Weber–Morris model. Freundlich adsorption isotherm constant is equal Kf = 30.62 mg/g and heterogenity factor n = 3.58. Sorption rate constant is k3 = 0.288 mg/(g·min1/2) and intraparticle diffusion rate constant C = 0.174 mg/g. Thermodynamic parameters such as free Gibb’s energy change (ΔG°), enthalpy change (ΔH°), entropy change (ΔS°) and energy activation Ea were determined. Calculated value of activation energy is equal 25.75 kJ/mol. The adsorption process of Ru(III) was found to be both spontaneous and thermodynamically preferable.

Studying removal of anionic dye by prepared highly adsorbent surface hydrogel nanocomposite as an applicable for aqueous solution

In this study, a Sodium alginate-g-poly (acrylamide-clay)/TiO2 hydrogel nanocomposite [SA-g-p(AM-Bn)/TiO2] was synthesized using the biopolymer sodium alginate (SA), acrylamide (AM), and bentonite clay (Bn) as hybrid materials embedded with titanium dioxide nanoparticles (TiO2NPs) for the removal of toxic Congo Red (CR) dye from an aqueous solution. The [SA-g-p(AM-Bn)/TiO2] nanocomposite has been described on the basis of thermal stability, morphological analysis, estimation of functional group, and crystalline/amorphous character by TGA, EFSEM/EDX, TEM, FT-IR, and XRD analysis, respectively. The effects of operational parameters toward the CR dye adsorption on [SA-g-p(AM-Bn)/TiO2], including contact time, adsorbent dosage, initial concentration, initial pH, and temperature were investigated. The maximum adsorption efficiency was found to be 185.12 mg/g for [SA-g-p(AM-Bn)/TiO2] in 100 mg/L of solution CR at pH 6.0 within 1 h. The equilibrium isotherms, kinetics, and thermodynamics parameters of adsorption were examined, and results showed that the isotherm fitted the Freundlich model and the kinetics adsorption model of CR followed pseudo-first-order, thus indicating physisorption of anionic-CR onto the sorbent due to the development of an electrostatic attraction bond. Thermodynamic parameters for [SA-g-p(AM-Bn)/TiO2] have values (ΔG and ΔH) reflecting the spontaneous and endothermic nature of the adsorption processes. Moreover, [SA-g-p(AM-Bn)/TiO2] presented outstanding excellent reusability and recyclability with a relatively best removal percentage as compared to [SA-g-p(AM-Bn)] and suggested their applicability towards the textile industry and water purification purposes.

Reactive Blue 19 Adsorption on Activated Carbon From Pumpkin (Cucurbita Pepo) Seed Waste: Kinetic, Isotherm and Thermodynamic Studies

In this study, the removal of Reactive Blue 19 dyestuffs in aqueous systems was investigated by adsorption method using activated carbon obtained from the pumpkin seed waste. Activated carbon obtained from pumpkin seed waste functionalized with ZnCl2 was used as an absorbent. Pumpkin seed hydrochar was characterized by FT-IR, SEM, TGA-DTA, BET, and XPS. In the experimental stages, the adsorption equilibrium time was determined as 45 minutes, the adsorbent dosage was 0.8 g and the optimum pH was 6.0. After this step, the adsorption parameters of Langmuir, Freundlich, Temkin, and Dubinin-Radushkevich isotherms were investigated. It has been pointed out that the adsorption process fits better with the Freundlich isotherm model, and the adhesion occurs in a multilayered manner and on a heterogeneous surface. Freundlich and Dubinin-Radushkevich isotherms support that the bonding mechanism is realized by physical interactions. When the kinetic data were evaluated, it was found to be compatible with the pseudo-second-order kinetic model. The thermodynamic parameters of adsorption indicate that the system is endothermic, and the adsorption of Reactive Blue 19 on activated carbon is a spontaneous process.

Anionic Dye Removal with a Thin Cationic Polyaniline Coating on Cellulosic Biomaterial.

This paper reports the development of novel adsorbent materials using polyaniline (PANI) grafted onto Posidonia (POS) fibers, aimed at efficiently removing phenol red (PSP), an anionic dye, from aqueous solutions. The synthesis involved the copolymerization of aniline grafted on the surface of the POS and aniline monomer in solution, resulting in a chemically bound thin PANI layer on the POS bioadsorbent. Structural characteristics and binding affinities of these adsorbents with PANI under its emeraldine salt (POS@PANI-ES) or emeraldine base (POS@PANI-EB) forms are reported. The rapid adsorption kinetics observed are attributed to enhanced accessibility to PANI adsorption sites on the POS surface. The binding percentages of PSP to POS@PANI-ES and POS@PANI-EB materials were found to be 97 and 50%, respectively, after 15 min of contact time. The Langmuir model for localized adsorption sites and the Volmer model for nonlocalized adsorption as a mobile layer were fitted to the experimental adsorption isotherms of PSP to POS@PANI-EB and POS@PANI-ES, yielding the thermodynamic parameters of adsorption. The adsorption capacities of PSP on POS@PANI-EB and POS@PANI-ES were 37.8 and 71.5 μmol g-1, respectively. The adsorption of PSP remained above 80% at moderate salt concentrations of around 0.1 mol L-1; however, higher concentrations of NaCl and CaCl2 in PSP solutions significantly reduced the adsorption on POS@PANI-ES.

Adsorption of copper (II) from aqueous solutions using adsorbent obtained with sodium hydroxide activation of biochar prepared by microwave pyrolysis

AbstractMicrowave heating is one of the leading methods that save energy, time, and cost for the conversion of bio-waste into biochar in the agricultural sector. In this study, in the first stage, economical biochar production from pistachio green hulls by microwave heating method is in question. In the second step, sodium hydroxide(NaOH) activation was followed to improve the surface properties of biochar. This adsorbent obtained was applied to remove copper ions(Cu(II)) from wastewater. Fourier-transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM), energy dispersive X-ray analysis (EDX), thermogravimetry differential thermal analysis (TG/DTG), and nitrogen adsorption/desorption methods were used to characterize the biochar samples. In adsorption studies, kinetic, isotherm, and thermodynamic parameters were investigated. Cu(II) adsorption capacity on modified biochar obtained by Langmuir isotherm was found to be 227.27 mg/g. In addition, the mechanism of Cu(II) adsorption on modified biochar has been proposed. Biochar, which is obtained from the green shells of pistachios, which is widely available and grown in Turkey, by microwave method and then NaOH activation, is a potential solution for both the improvement of water pollution caused by heavy metals and the disposal of related wastes with an appropriate method.

Poly O-toluidine-coated acetic acid modified eggshell-chitosan with ZnFe2O4 nanoparticles as a new and promising sorbent nanocomposite for rapid removal of toxic dyes such as Brilliant Green and Acid Red from the aquatic environment

The conversion of organic waste into valuable commodities is essential for safeguarding the environment and promoting the sustainable development of the economy. This investigation centres on the production of Zinc ferrite nanoparticles (ZnF NPs), modified eggshells (MES) impregnated with chitosan (CS) and coated with poly ortho-toluidine P(OT) nanocomposites (NCs). This synthesis involves a quaternary composition denoted as P(OT)/MES/CS/ZnF NCs, achieved through chemical polymerization techniques. The resulting NCs were characterized and applied for the removal of Brilliant Green (B.GR) and Acid Red (A.RE). Four distinct compositions, namely pure P(OT), binary P(OT)/MES, ternary P(OT)/MES/CS, and quaternary P(OT)/MES/CS/ZnF NCs, were synthesized. The outcomes revealed that the quaternary P(OT)/MES/CS/ZnF NCs exhibited the highest adsorption capacities for B.GR and A.RE at)27.03 and 142.8 mg−1(, respectively. The findings revealed that the most favorable parameters for the removal of A.RE were attained at a pH of 2, using 15 mg of P(OT)/MES/CS/ZnF NCs at a concentration of 25 mg/L for a duration of 120 min. On the other hand, when it comes to removing B.GR, the best results were shown while using 15 mg of P(OT)/MES/CS/ZnF NCs at a concentration of 5 mg/L for 120 min, specifically at a pH of 6. The greatest real wastewater removal efficiencies for A.RE dye and B.GR dye, respectively, were found to be 99.5% and 97.6% under these operating circumstances. These optimal quaternary NCs demonstrated the ability to be regenerated four times without significantly compromising their adsorption properties and exhibited a remarkable capacity to remove 96–98% of dyes from real polluted water. Through the use of regression data and a pseudo-second-order model, the adsorption kinetics were explained, with R2 values of 0.994 for A.RE and 0.993 for B.GR, respectively. Thermodynamic parameters of dye adsorption by the NCs affirmed the fact that adsorption occurs spontaneous and have endothermic nature. This study underscores an effective synthesis approach applicable for large-scale production of new adsorbents for water treatment purposes.

Experimental and modeling studies on the removal of bromocresol green from aqueous solutions by using pine cone-derived activated biochar

AbstractThis study was carried out to evaluate the potential application of pine cone (PC)-derived activated biochar which has a surface area of 1714.5 m2/g for bromocresol green (BCG) dye removal from aqueous solution. Batch adsorption experiments involved varying pH, temperature, contact time, adsorbent dosage, and initial dye concentrations and the maximum BCG removal (96.27%) occurred at pH: 2.0, T: 45 °C, m: 2 g/L, t: 15 min., and Co: 25 mg/L. To study the characteristics of adsorption, the adsorption kinetic isotherm and thermodynamic parameters were employed. The experimental data was evaluated to fit well with the Temkin isotherm (R2 = 0.99) and the adsorption process followed pseudo-first-order kinetics (R2 = 0.96). Thermodynamic parameters obtained from the adsorptive uptake showed that the interaction was endothermic and spontaneous in nature. The regenerated activated PC biochar showed good performance (95.0%), even, after 4th regeneration. To predict the BCG adsorption capacity of activated PC biochar, many different artificial neural network (ANN) models have been developed. The optimal ANN model gave mean absolute error (MAE), mean bias error (MBE), root mean square error (RMSE), and R2 values of 0.036, 0.578, 0.947, and 0.999, respectively. The results obtained showed that ANN can be used to effectively model the BCG adsorption process.

Mining Ag+ ions from wastewater with Bio-MOF-1: From adsorption to high value-added application

In this work, Bio-MOF-1 was adopted to remove and recover the Ag+ ions in the corresponding wastewater, which exhibited excellent Ag+ ions adsorption ability with adsorption capacity up to 655.3 mg/g. The adsorption kinetics, isotherm and thermodynamic parameters confirmed the adsorption process was dominated by multilayer chemisorption. The Ag+ ions adsorption behavior over Bio-MOF-1 was spontaneous, exothermic and orderly. In addition, Bio-MOF-1 displayed efficiently selective sorption toward Ag+ with the presence of the co-existence ions (including Cu2+, Ni2+, Co2+, Zn2+, Pd2+, Cd2+, Pt2+ and Au3+), in which the selective sorption efficiency could reach > 99.9% toward Ag+ with the distribution coefficients up to 1.4 × 107 mL/g. The possible adsorption mechanism of Bio-MOF-1 towards Ag+ mainly involved ion exchange, electrostatic and coordinative interactions, which was further analyzed by both experimental determination and Density Functional Theory (DFT) calculations. In particular, the Bio-MOF-1 adsorptively saturated with Ag+ could be used as the antimicrobial agent for long time (40.0 h) inhibition of the Escherichia coli (E. coli) growth. This work proposed and affirmed the possibility that mining resource was recovered from wastewater to produce the highly valued products.

Recyclable magnetic nickel ferrite–carboxymethyl cellulose–sodium alginate bio-composite for efficient removal of nickel ion from water

In waste water treatment, magnetic bio-composites are frequently investigated as an adsorbent recently due to their great capacity for adsorption and affordability. In this current work, an attempt has been made to develop spinel nickel ferrite–carboxymethyl cellulose (NiFCMC) composite and modified its surface by alginate polymer to form NiFCMC–Alg composite. Several techniques were utilized to characterize these adsorbents including Fourier transform infrared spectroscopy, x-ray diffraction, field emission scanning electron microscopy, energy-dispersive spectra, thermogravimetric analysis, vibration sample magnetometry and pH of point zero charge. These adsorbents were explored to check their potentiality to remove Ni (II) ions in aqueous medium on various parameters such as contact time, initial metal ion concentration, pH, adsorbent dose and temperature. The optimum time for establishment of equilibrium was 180 minutes at pH 8 with adsorbent dose of 0.1 g. Results of kinetic studies revealed that the best fit for the metal ion adsorption data was the Lagergren pseudo-second-order mode indicating the chemisorption nature. Likewise, the Langmuir isotherm model also showed good agreement with adsorption equilibrium data with maximum adsorption capacities 47.84 ± 2.39 and 60.24 ± 3.01 mg/g for NiFCMC and NiFCMC–Alg respectively. The calculated adsorption thermodynamic parameters confirmed the spontaneous nature of adsorption process. The regeneration efficiency of both adsorbents was studied for five cycles and showed significant results. This study has shown that NiFCMC and NiFCMC–Alg can be a good substitute for removing Ni (II) ions in aqueous medium.

Magnetic dummy-template molecularly imprinted polymer with an ultrathin shell for selective enrichment of geosmin in water sample

A dummy-template molecularly imprinted polymer (DMIP) based on magnetic carbon nanotubes was synthesized. The eluted polymers with an improved ultrasound assisted/oscillating (magnetic separation) method were successfully employed for the adsorption and separation of geosmin (GSM), an odorous compound in eutrophic waterbodies. The properties of the obtained composite materials were evaluated through a series of morphological and physicochemical characterization. The results showed that a thin and uniform imprinted shell (∼10–15 nm) effectively coated the surface of magnetic carbon nanotubes, exhibiting good adsorption efficiency and magnetic functionality. The binding performance and selectivity of Mag-MWCNTs @DMIPs as adsorbents for GSM were evaluated and compared with non-imprinted polymers. The maximum adsorption capacity of polymers for GSM, as determined by the Langmuir model, is 18.71 mg g−1, which adsorption equilibrium reached in approximately 45 min. The adsorption thermodynamic parameters ΔG shown that the adsorption process was spontaneous. Selectivity and regeneration experiment further demonstrated the ability of Mag-MWCNTs @DMIPs to selectively separate trace GSM from complex matrices. The polymer obtained in this study can be used as an adsorbent for magnetic dispersion solid-phase extraction to preconcentration of trace GSM in natural water, facilitating the measurement of GSM.

Single and multicomponent adsorption of amoxicillin, ciprofloxacin, and sulfamethoxazole on chitosan-carbon nanotubes hydrogel beads from aqueous solutions: Kinetics, isotherms, and thermodynamic parameters

The removal of antibiotics in water receiving bodies is an integral part in eradicating antimicrobial resistance which has become a major threat to public health. Solid-liquid adsorption has demonstrated to be an effective technique in the removal of antibiotics from aqueous environments. Herein, chitosan-carbon nanotube (chitosan-CNT) hydrogel beads were synthesised for the adsorption of amoxicillin (AMX), ciprofloxacin (CIP) and sulfamethoxazole (SMX) from aqueous solution. Adsorption kinetics, isotherms and thermodynamic parameters were systematically investigated at a solution pH of 7. Single adsorption kinetics findings suggest that experimental data for AMX, CIP and SMX was better fitted by the nonlinear pseudo-first order model with calculated maximum adsorption capacities of 23.1 mg.g−1, 23.7 mg.g−1 and 25.17 mg.g−1, respectively. Moreover, findings from the Weber-Morris kinetic model suggest that multiple processes were limiting the overall adsorption rate of AMX, CIP and SMX on chitosan-CNT. Adsorption isotherm results indicated that single adsorption experimental data was better fitted by the nonlinear Freundlich isotherm model, while binary and ternary system experimental data were better fitted by the nonlinear competitive extended Sips adsorption isotherm models. Moreover, results for binary and ternary adsorption showed that multicomponent adsorption systems exhibited both antagonistic and synergistic adsorption of AMX, CIP and SMX. From the thermodynamics fundings, it was evident that the adsorption of AMX, CIP and SMX from solution is an endothermic process governed by both physical and chemical adsorption mechanisms. Based on the findings of the current study, it was concluded that chitosan-CNT has potential as a green technology for the removal of antibiotics from solution.

Green synthesis of Dextrin‐graft‐poly(allyl amine‐co‐methacrylic acid)/reduced graphene oxide composite and its application for dye and pesticide removal from the aqueous medium

AbstractA Dextrin‐graft‐poly(allyl amine‐co‐methacrylic acid)/reduced graphene oxide (DEXTGP/RGO) is synthesized through the grafting of a combination of allyl amine (AAM) and methacrylic acid (MAA) monomers onto the dextrin polysaccharide backbone by using the free radical copolymerization technique in an aqueous medium, with potassium peroxydisulfate serving as the initiator followed by the partial reduction of graphene oxide (GO). Various characterization techniques including FTIR, 1H/13C NMR, XRD, FESEM, EDAX, and BET analysis are utilized to characterize both the synthesized DEXTGP/RGO composite and graft copolymer. Investigations are conducted on multiple operational variables, including adsorption kinetics, isotherms, and thermodynamic parameters, for the adsorption of both MB and PL. Both intra‐particle diffusion kinetic model and pseudo‐second‐order kinetics are observed to follow for the adsorption of MB, while the Langmuir isotherm model provided a good fit for the equilibrium data. In contrast, the adsorption of PL displayed solely pseudo‐second‐order kinetics, while the equilibrium data shows good agreement with both the Langmuir and Dubinin‐Radushkevich isotherm models. Maximum adsorption capacity ( ) of the RGO composite is found to be 932.56 mg/g for MB and 311.63 mg/g for PL. The thermodynamic analysis revealed that the adsorption of dye and pesticide onto the RGO composite is a spontaneous process.

Temperature Dependence of Adsorption and Effectiveness for a Pyrimidinium-Type Corrosion Inhibitor on Mild Steel

In the oil and gas industry, produced water with a high dissolved salt content is a common byproduct of hydrocarbon extraction from conventional and unconventional wells. Other than salts, corrosive gases such as CO2 are abundant in the production stream, which dissolve and acidify the solution, posing a risk of internal pipeline corrosion. To mitigate this issue, injection of corrosion inhibitors has emerged as a cost-effective approach. In various aggressive conditions, heterocyclic molecules that contain nitrogen atoms have proven to be highly effective corrosion inhibitors for many alloys. In this study, tetrahydropyrimidinium (THP-C14) inhibition efficiencies were investigated at temperatures of 25°C, 55°C, and 80°C using electrochemical methods, including linear polarization resistance and potentiodynamic sweeps. Corrosion inhibition data were then correlated with THP-C14 concentration, using the five adsorption isotherms: Langmuir, Temkin, Frumkin, Flory-Huggins, and Dhar-Flory-Huggins models. These isotherms utilize different assumptions to establish the correlation between coverage and inhibitor concentration. The suitability of these five isotherm models for describing the corrosion inhibition behavior of THP-C14 was examined. In addition, the thermodynamic parameters (Kad, ΔadGo) of adsorption for THP-C14 at 25°C, 55°C, and 80°C were calculated and compared using the aforementioned adsorption isotherm models. Finally, a mechanism was proposed for the adsorption behavior of the THP-C14 corrosion inhibitor model compound. Chloride ions were important for inhibitor adsorption.

Facile fabrication of highly efficient bifunctional polydopamine–polyethyleneimine copolymerization‐modified magnetic material and its effective applications for both adsorption of gold ions and catalytic reduction of 4‐nitrophenol

AbstractThe heavy metal ions and organic pollutants are major harmful substances in wastewater because of their toxicity on human health and environment. Nowadays, the adsorption–catalysis treatment to remove them simultaneously is still a challenge because of their different reaction mechanisms. Herein, a novel bifunctional polymer magnetic material Fe3O4@PDA‐PEI was successfully developed through a facile co‐deposition method by the copolymerization modification of polydopamine (PDA) and polyethyleneimine (PEI) on magnetic ferroferric oxide, which can both be utilized for both heavy metal ion removal from simulated industrial wastewater and further effective catalytic reduction of toxic 4‐nitrophenol (4‐NP) to useful 4‐aminophenol. The maximum adsorption capacity of Fe3O4@PDA‐PEI for gold ions was 465.12 mg/g at 35°C, and the adsorption thermodynamic parameters ΔG, ΔH, and ΔS of Fe3O4@PDA‐PEI (m(PDA):m(PEI) = 2:1) were −5.28 (35°C), 25.58, and 111.30 J K−1 mol−1, respectively. In addition, a sustainable strategy of converting gold ions to gold nanoparticles has been demonstrated for additional catalytic functionality of Fe3O4@PDA‐PEI, and Fe3O4@PDA‐PEI‐Au could effectively catalyze the reduction of 4‐NP at ambient temperature within 9 min. Fe3O4@PDA‐PEI with the advantages of facile fabrication, easy separation, excellent adsorption, and catalysis performance could be used as a promising polymer composite material in complicated wastewater environment. © 2023 Wiley Periodicals LLC.

Development of 1-phenyl-3-(4-(pyridin-4-ylmethyl)phenyl)urea derivatives as robust corrosion inhibitors for mild steel in 1 M HCl environment: Insight from ,molecular, experimental, and microscopic-scale modelling approaches

Cost-effective, novel urea derivatives, 1-phenyl-3-(4-(pyridin-4-ylmethyl)phenyl)urea (U-1), 1‐(4‐fluorophenyl)‐3‐(4‐(pyridin‐4‐ylmethyl)phenyl)urea (U-2), and 1‐(4‐methylphenyl)‐3‐(4‐(pyridin‐4‐ylmethyl)phenyl)urea (U-3) were synthesized to investigate as the corrosion inhibitors for mild steel/1 M HCl interface. Inhibition efficiency increases with the increasing inhibitor’s concentration but decreases with increasing temperature. Thermodynamic adsorption and activation parameters demonstrate that the adsorption of inhibitors follows Langmuir isotherm via physicochemical interactions. Potentiodynamic polarization measurements reveal that the inhibitors are mixed-type, impeding the charge-transfer process. Surface analysis supports a thin inhibitor film formation on the mild steel. The maximum inhibition efficiency of U-1, U-2 and U-3 are 94.97 ± 0.38%, 93.60 ± 0.62% and 97.42 ± 0.48% respectively. The calculated electrochemical impedance spectra (EIS) parameters such as ohmic resistance, double layer capacitance, relaxation time, effective thickness, and conductivity of grain and grain boundary are in-line with the efficiencies of NHUs. The performance of corrosion inhibitors follows a sequence U-3 > U-1 > U-2, emphasizing the influence of the substituent’s inductive effect (-CH3 > -H > -F) in inhibitors. Density functional theory (DFT) was performed to understand the correlation between molecular structure and inhibition efficiency. The Fukui indices confirm the presence of local attacking sites on the metal surface where inhibitors attack. A molecular dynamic (MD) simulation is used to determine the interaction energies between the inhibitors and mild steel. Radial Distribution Function (RDF) measurements confirm the existence of the chemical nature of the interaction. Furthermore, the diffusion coefficient of corrosive particles, self-diffusion coefficient of inhibitors, fractional free volume (FFV), and interaction between inhibitor’s film and corrosive particles are examined. Theoretical studies support experimental results.

Cauliflower stem-derived biochar for effective adsorption and reduction of hexavalent chromium in synthetic wastewater: A sustainable approach

Contamination with hexavalent chromium (Cr(VI)) has drawn immense interest of national and global regulatory authorities due to its toxic and carcinogenic threat. Although various approaches have been applied for Cr(VI) removal from aqueous solution, adsorption has been proven to be the most promising method. Biochar, a cost-effective adsorbent, is one of the prominent adsorbents for environmental remediation that can be produced from different biowaste precursors. Cauliflower (Brassica oleracea) is one of the common vegetables around the world. The cauliflower stem is not commonly edible and therefore discarded as waste. In this work, the cauliflower waste-based biochar, with and without chemical modification, was prepared from a simple oxygen-limited pyrolysis. With the assistance of TGA, DSC, and SEM-EDS, the effect of pyrolysis temperature on the generation of biochar, reaction energy as well as reaction temperature, and morphology of the prepared biochar were analyzed. Pyrolytic temperature of 450°C was found to be the best for tailoring biochar. Chromium(VI) removal from the synthetic solution was performed by using biochar as an adsorbent. H3PO4-activated biochar (PBC) performs better than other biochar. The adsorption kinetics, isotherm, and thermodynamic parameters were studied in batch-wise experiments by varying the contact time, initial Cr(VI) concentration, and operating temperature. The Cr(VI) removal on PBC biochar follows a pseudo-second-order kinetics and fits with Langmuir isotherm resulting in Cr(VI) adsorption capacity of 64.10 mg/g. The thermodynamic parameters and XPS analysis of spent biochar adsorbent reveal that Cr(VI) reduction to Cr(III) happens simultaneously during the removal process. The spent biochar can be regenerated using 0.1 M NaCl and used for several cycles. Thus, the cauliflower stem-derived biochar can be effectively applied for Cr(VI) removal for multiple cycles through regeneration, which would contribute to the circular economy for environmental purposes.

Tyramine Adsorption Using the Modification of Takari Natural Sand-Based Silica with Bovine Serum Albumin (BSA)

In this article, we use a batch method to convey tyramine adsorption by modifying Takari natural sand-based silica with BSA and tyramine adsorption. The research stages include the optimization of adsorbent mass, pH, temperature, determination of the isotherm model, and thermodynamic parameters of tyramine adsorption. The tyramine concentration was determined using UV-Vis. The characterizations carried out were functional groups using FT-IR and surface morphology using SEM. The results of FT-IR characterization demonstrated the success of BSA modification, as observed in the C-H, N-H, and C-N groups, which are the typical functional groups of BSA. The SEM image of SiO2@BSA before tyramine adsorption revealed unevenly sized particles, uneven distribution, and agglomeration, leading to larger particles. The morphology of SiO2@BSA-tyramine appeared to be more uniform, exhibiting a smoother shape with a slightly uneven surface. The optimum pH was 5 (qe=11.74 mg/g), and the optimum temperature was 303 K (qe= 2.47 mg/g). The isotherm study showed that the adsorption adhered to the Redlich-Peterson isotherm model with an R2 value of 0.987 (qe=5.157 mg/g and n =3.759). The thermodynamic study demonstrated ∆Ho = 49.08 kJ/mol, ∆Go =-17.84; -20.05 and -22.26 kJ/mol, and ∆So =0.22 kJ/mol.K. These results indicated that the tyramine adsorption process on SiO2@BSA adsorbent occurred endothermically and spontaneously at the temperature of 303 K, and the adsorption was of a physical-chemical adsorption type.

Adsorption and desorption strategy for recovering β-carotene from crude palm oil: Kinetics, equilibrium and thermodynamics studies

Palm oil uses are widespread in several industry segments. During refining process, minor compounds such as carotenoids, phytosterols, squalene and tocotrienols are lost. The β-carotene is lost due to the bleaching and the high temperature in the deodorization step. The aim of this work is to recover β-carotene before its degradation in the refining process, using adsorption-desorption strategy. Batch adsorption studies were evaluated for five adsorbents: Diaion HP20, Sepabeads SP70, Sepabeads SP700, Diaion HP2MGL, Amberlite XAD7HP. Modeling of kinetics and equilibrium curves were performed for the Sepabeads SP70, which had the best performance in adsorption. The best conditions for adsorption were at the concentration of 30% (w/w) oil in isopropyl alcohol (IPA) micelle at 30 °C for 180 min. Thermodynamics parameters of adsorption revealed a favorable, spontaneous and exothermic process associated with physical bonding. The studies performed on adsorbent reutilization proved that the regeneration is effective and allows the material reuse at least for 5 cycles without changing the adsorption capacity. Additionally, desorption was evaluated in single and multiple steps and the final enrichment factor was 3.40 ± 0.21. This process allows the palm oil utilization for edible purposes after the adsorption step while recovering β-carotene based on its physicochemical characterization.