Adsorption of antiretroviral drugs, abacavir, nevirapine, and efavirenz from river water and wastewater using exfoliated graphite: Isotherm and kinetic studies

In this work, exfoliated graphite was used to adsorb antiretroviral drugs from river water and wastewater. The exfoliated graphite was prepared from natural graphite by intercalating it with the acids and exfoliating it at 800 °C. It was characterized using Fourier Transform Infrared Spectroscopy which showed phenolic, alcoholic, and carboxylic functional groups between 1000 cm-1 and 1700 cm-1. Energy-dispersive X-ray spectroscopy results showed carbon as the main element with splashes of oxygen. The Scanning Electron Microscopy images showed increased c-axis distance between graphene layers after intercalation, which further increased after the exfoliation. The exfoliation resulted in elongated distorted cylinders, which were confirmed by the lower density (0.0068 g/mL) of exfoliated graphite material compared to the natural graphite (0.54 g/mL). The X-ray diffraction pattern showed the characteristics of hexagonal phase graphitic structure by the diffraction plane (002) at 26.74°. Raman spectroscopy results showed the natural graphite, graphite intercalated, and exfoliated graphite contained the D, G, D', and G' peaks at about 1350 cm-1, 1570 cm-1, 2440 cm-1, and 2720 cm-1, respectively indicating that the material's crystallinity was not affected by the modification. The highest antiretroviral drugs removal (95-99%), from the water was achieved with a solution pH of 7, an adsorbent mass of 30 mg, and an adsorption time of 30 min. The kinetic model and adsorption isotherm studies showed that the experimental data fit well in pseudo-second-order kinetics and is well explained by Freundlich's adsorption isotherm. The maximum adsorption capacity of the exfoliated graphite for antiretroviral drugs ranges between 1.660 and 197.0, 1.660-232.5, and 1.650-237.7 mg/g for abacavir, nevirapine, and efavirenz, respectively. The obtained removal percentages were 100% in river water, 63-100% in influent and 70-100% in effluent wastewater unspiked samples.

IntraPD model: Leaching of heavy metals from naturally contaminated soils

This paper presents a novel method for predicting the migration of heavy metal contaminants in soils that contain heavy metal pollutants deep within the particles, which may cause delayed leaching. The proposed approach, the intraparticle pore-diffusion (IntraPD) model, incorporates both intraparticle diffusion and sorption equilibrium and is utilized to simulate batch leaching tests of heavy metal-contaminated soils using the finite difference method. The IntraPD model can solve the leakage of heavy metals from contaminated soil particles of arbitrary particle size distribution as a one-dimensional, polar-symmetric problem in the spherical coordinate system, assuming the soil particles to be porous perfect spheres. The findings from the simulation demonstrate a notable impact of soil particle size distribution on both the leaching rate and the amount of contaminants. Specifically, the coefficient of uniformity, which indicates the ratio of the maximum to minimum particle size, was identified as a significant factor influencing the leaching rate. When the coefficient of uniformity is less than or equal to 5, it has a combined effect on the leaching rate. However, when the coefficient of uniformity exceeds 5, the maximum particle size becomes the primary determinant of the leaching rate. The proposed model provides a valuable tool for accurately simulating batch leaching tests of naturally contaminated soils with diverse particle size distributions.

Rethinking of the intraparticle diffusion adsorption kinetics model: Interpretation, solving methods and applications

Adsorption is a widely used unit process in various fields, such as chemical, environmental and pharmaceutical, etc. The intraparticle diffusion adsorption kinetics model is one of the most widely used adsorption kinetics models. However, the application and solving method of this model have yet to be discussed. This model has two forms (q_t = kt^1/2 and q_t = kt^1/2 + constant, where q_t is the adsorption capacity at time t, k and constant are the model parameters), which have not been unified yet. Moreover, the interpretation of this kinetics model lacks a theoretical basis (if the line passes through the origin point (0, 0), the adsorption is dominated by the intraparticle diffusion; if not, it is a multiple adsorption process). In this study, we analyzed the proper equations of the intraparticle diffusion model and their applications, discussed the interpretation of the mass transfer steps revealed by this model, and provided the solving methods. The result indicated that the piecewise function q_t = k₁t^1/2 (0 ≤ t ≤ t₁); q_t - q_t = t1 = k₂(t - t₁)^1/2 (t₁ < t ≤ t₂) is the proper form of this model. The adsorbate diffusion in the pores inside the adsorbent is the mass transfer step revealed by this model. The statistical parameters should be used to evaluate the fitting results instead of judging whether the model lines pass through the origin point (0, 0). We provide the solving methods to use the Origin and Microsoft EXCEL software to solve the model. Our study established the method for application of the intraparticle diffusion model.

Estimation of sorption-desorption characteristics of biosorbent of Lantana camara leaves for removal of Pb (II) ions from wastewater

This study points out the method regarding the removal of Pb (II) ions from water by treatment with Lantana camara leaves' biosorbent (LCLB). The sorption process was investigated by varying different parameters pH, contact time, adsorbent dose, initial metal ion concentration, and temperature. For a 5.00 g sorbent dose and a 45 min of the contact period, a Pb (II) ion solution with an initial metal ion concentration of 10 mg/L resulted in 90.7% maximum elimination at an optimum pH 6 and temperature 298 ± 1.5 K with LCLB. The adsorption process was spontaneous and exothermic. The maximum monolayer adsorption was 3.5 mg/g for Pb (II) sorption using LCLB. Adsorption of Pb (II) ions using LCLB (R² > 0.999) followed the pseudo-second-order kinetics. The spectroscopic characterization was done by fourier transform infrared (FT-IR) analysis, while scanning electron microscope (SEM) images were captured for the morphological characterization. Desorption experiments revealed that hydrochloric acid has a strong potential as an eluent for Pb (II) ion desorption. The findings proposed that LCLB can be used as an effectual and cost-effective biosorbent for the expulsion of Pb (II) ions.

Preparation and characterization of low-cost nano-particle material using pomegranate peels for brilliant green removal

A low-cost nano-particle material was successfully prepared using waste pomegranate peels. Batch adsorption experiments were carried out to investigate the effect of different operating conditions on the removal of brilliant green (BG) dye from an aqueous solution. SEM images of pomegranate peels nano-particles (PPNP) declared roughness of the surfaces and TEM images indicated a spheroid shape with an average particle size of 37 nm. The specific surface area of the PPNP was 354.46 m²/g and the particle size had a mean diameter of 613.4 nm. The active nano-particle suspension showed a net negative charge (-29 mV) at natural pH. The XRD pattern of PPNP displayed an average crystallite size of 13.50 nm and EDS analysis shows that the PPNP consists of 83% carbon. The experimental work showed that the removal of BG had optimum removal efficiency at 20 min, 0.3 g adsorbent mass, 25 °C, and pH 8. The kinetic data can be described well with the pseudo-second-order model and the isotherm data was found to fit the Dubinin model. The thermodynamic study proved that BG adsorption on PPNP was physisorption (ΔG = -5.949 kJ/mol) and spontaneous at low temperature (ΔH = -17.193 kJ/mol, ΔS = -0.0382 kJ/mol. k)This study used an agriculture waste (pomegranate peels) to prepare an environmentally friendly and low-cost adsorbent within the nano-scale by thermal activation. The nano-particles prepared were shown to be a promising adsorbent, demonstrating high surface area and well-developed porosity. The prepared adsorbent will have a great impact on wastewater treatment technology and possible applications at a large scale.

Adsorptive Capacity of Calcinated Hen Eggshell Blended with Silica Gel for Removal of Lead II Ions from Aqueous Media: Kinetics and Equilibrium Studies

In this study, a description was given for the adsorbent CaSiO₃ for allure proximate examination and determination like particle density, main part density, and porosity analysis. This is performed before management of batch adsorption experiments. Both kinetics and balance studies for the adsorbent were examined. The influences of various process parameters like lead concentration, pH, adsorbent dosage, and contact temporal length for process removal were explored. The removal efficiency of CaO from eggshell was enhanced to increase after mixing it with silica coagulate compared with added scholar's findings for the same limit. The maximum removal efficiency (99.58%) was obtained by limiting the pH, adsorbent dosage, initial lead concentration, and contact time at 4, 1.8 g, 35 g/L, and 140 minutes, respectively. Thus, blending CaO from eggshells with silica gel can increase the adsorption competency of CaO. Lead removal is well integrated into the Langmuir isotherm model with an equivalent factor of 0.991. The kinetic data of adsorption fit well into a pseudo-first-order model with a correlation coefficient of 0.90111. The pseudo-second-order model was the rate-determining step involved in the lead adsorption process for calcium silicate (CaSiO₃) adsorbents.

Techno-economics of coconut coir bioadsorbent utilization on free fatty acid level reduction in crude palm oil

The quality of crude palm oil (CPO) is generally determined by the levels of free fatty acids (FFA). This helps in balancing the level of acidity during transportation and storage processes. However, high FFA in CPO is not good for consumer health. One of the methods for adsorbing FFA is adsorption, which is the adhesion of atoms, ions, or molecules from a gas, liquid, or dissolved solid to a surface. Therefore, this study aims to analyze the effect of contact time (40, 80 and 120 min) and Coconut Coir (CC) bioadsorbent concentrations of 1, 2 and 3 (%, w/v) on the reduction of CPO FFA levels. This began with the activation of CC biochar synthesis by using NaOH and HCl, which produced CC-NaOH and CC-HCl bioadsorbents based on the product of NaOH. Furthermore, the adsorption process was carried out by mixing CPO with CC-NaOH and CC-HCl bioadsorbents in a three-necked flask. After this, the filtrate product was obtained and analyzed for its FFA levels. The results showed that the largest percentage reduction for the effect of bioadsorbent concentration was 3% (w/v) at a contact time of 120 min. It also indicated that this study enabled lower levels of FFA in CPO. Based on the detailed cost estimate, the production cost of the CC-NaOH bioadsorbent was USD 481,874, sold at USD 95/ton with annual sales and net profit (after tax) at USD 684,000 and USD 141,188, respectively. This profit after tax and rate of return on investment was found to be 20.68 and 39.49% of the entire estimation, respectively. It also had a payback period of 2.95 years and a break-even point at a capacity of 43.16%. In addition, the prepared adsorbent showed significant ability as an inexpensive, reproducible and environmentally friendly compound used in reducing the FFA levels of CPO.

Adsorption Behavior of Methylene Blue Dye by Novel CrossLinked O-CM-Chitosan Hydrogel in Aqueous Solution: Kinetics, Isotherm and Thermodynamics

The chemical cross-linking of carboxymethyl chitosan (O-CM-chitosan), as a method for its modification, was performed using trimellitic anhydride isothiocyanate to obtain novel cross-linked O-CM-chitosan hydrogel. Its structure was proven using FTIR, XRD and SEM. Its adsorption capacity for the removal of Methylene Blue (MB) dye from aqueous solution was studied. The effects of different factors on the adsorption process, such as the pH, temperature and concentration of the dye, in addition to applications of the kinetic studies of the adsorption process, adsorption isotherm and thermodynamic parameters, were studied. It was found that the amount of adsorbed MB dye increases with increasing temperature. A significant increase was obtained in the adsorption capacities and removal percentage of MB dye with increasing pH values. An increase in the initial dye concentration increases the adsorption capacities, and decreases the removal percentage. It was found that the pseudo-second-order mechanism is predominant, and the overall rate of the dye adsorption process appears to be controlled by more than one step. The Langmuir model showed high applicability for the adsorption of MB dye onto O-CM-chitosan hydrogel. The value of the activation energy (E_a) is 27.15 kJ mol⁻¹ and the thermodynamic parameters were evaluated. The regeneration and reuse of the investigated adsorbent was investigated.

Removal of reactive orange 16 and reactive green 19 using Cyphos IL101-impregnated Amberlite XAD7HP resin in batch and recirculating stirrer vessel

Reactive dyes are highly soluble in water, and carcinogenic. Therefore, it is essential to remove these dyes from their aqueous solutions. This study focused on the simultaneous removal of reactive orange 16 (RO) and reactive green 19 (RG) dyes from their binary dye solution using Cyphos IL101-impregnated Amberlite XAD7HP resin (ILX7) in batch and recirculating stirrer vessel (RSV). In the batch study, the experimental operating conditions were designed by using central composite design of response surface methodology. Influence of important input variables (RO dye concentration, RG dye concentration, pH, and resin dosage) on the dye adsorption was studied and their values were optimized. At the optimum values of input variables, equilibrium, kinetic, and thermodynamic studies were performed for the binary dye mixture. The equilibrium and kinetic adsorption data were best fitted with extended-Freundlich and pseudo-second-order models, respectively. Now to intensify the process, continuous studies were performed in a RSV at optimum conditions and at different flow rates and stirring speeds. The impregnated resin was regenerated by using 80% v/v ethanol and successfully reused up to 3 cycles with slight decrease in the adsorption capacity.

Equilibrium, kinetics and thermodynamics of lead (II) adsorption in bioadsorvent composed by Caryocar coriaceum Wittm barks

The improper disposal of waste containing toxic metals promotes serious environmental problems. Biosorption stands out as a powerful technique in removing toxic metals from aqueous solutions, making it an efficient and low-cost technique, since it makes use of abundant materials and of natural origins. This work aimed to study the application of the bark of Caryocar coriaceum Wittm, as a possible bioabsorbent for the removal of Lead (II) present in aqueous solutions, for this, residues of this material were collected in a public market, where they were washed and dried, then crushed, sieved (32mesh) and washed again, to then be used in the kinetic, isotherm and thermodynamic tests of lead (II) ions adsorption. After the experiments, it was found that the increase of the temperature disfavored the rate of lead (II) adsorption, ranging from 15.6 to 13.5 mg.L^-1, for temperatures of 5 °C and 35 °C, respectively. The pseudo-second order kinetic model best characterizes the adsorption velocity obtaining a linear regression coefficient of 0.9997, while the pseudo-first order obtained a value of 0.7117. Adsorption occurred by chemisorption, with intra-film diffusion. The isothermal model that best represented the adsorption was Langmuir's (R² 0.99). It was concluded that the bark of Caryocar coriaceum Wittm is a good alternative to be used as a bioabsorbent for solutions containing dissolved lead (II).