Comparison of the nonlinear and linear forms of the van't Hoff equation for calculation of adsorption thermodynamic parameters (∆S° and ∆H°)

Adsorption of Indigo Carmine dye onto the surface-modified adsorbent prepared from municipal waste and simulation using deep neural network

A new adsorbent was prepared from municipal wastes (a mixture of Corn Stover, Paper Waste, and Yard Waste) by cationization with 3 ̶ Chloro ̶ 2 ̶ Hydroxypropyl Trimethylammonium Chloride. The FTIR spectrum confirmed the quaternary ammonium group's presence on the adsorbent surface (1450 cm^-1). The maximum adsorption capacity (148 mg/g) was higher than the earlier reported values. Liu isotherm described well the adsorption process, with a high R²_adj value (0.997). The pseudo-first-order equation fits well for kinetic data, and thermodynamic experiments demonstrated the endothermic nature of the adsorption. The deep neural network (DNN) is applied to simulate the adsorption process, which outperformed the classical machine learning and shallow neural network models. The DNN model predicted accurately the adsorption process with the lowest deviation from the actual values with Mean Absolute Error (MAE = 3.2), Root Mean Squared Error (RMSE = 4.89), and the highest performance accuracy of R² (0.96) as compared to various classical ML algorithms such as Linear Regressions (MAE = 12.53, RMSE = 18.01, R² = 0.42), Random Forest (MAE = 5.81, RMSE = 10.05, R² = 0.82), and Extra Trees (MAE = 4.35, RMSE = 8.22, R² = 0.88). The utilized DNN model can be used for predicting the removal efficiency of dyes for various combinations of input parameters without going through laboratory experiments.

Adsorption Separation of l-Tryptophan Based on the Hyper-Cross-Linked Resin XDA-200

l-Tryptophan (l-Trp) was separated from its aqueous solution by hyper-cross-linked resins. The adsorption and desorption performances of l-Trp on different resins were compared. The weakly polar resin XDA-200 was selected as an excellent adsorbent with high adsorption amount and easy elution. The resin has a high adsorption selectivity and strong salt resistance. The adsorption mechanism of l-Trp on resin XDA-200 was elucidated based on adsorption thermodynamics experiments, molecular dynamics simulations, and adsorption kinetics experiments. The dynamic separation process of l-Trp was finally studied. The adsorption of l-Trp on resin XDA-200 is a spontaneous process driven by adsorption enthalpy. l-Trp^± is the most favorable form for l-Trp adsorption on resin XDA-200 because of the strongest affinity of l-Trp^± to the resin and relatively low water solubility. The adsorption of l-Trp is mainly based on π-π and hydrophobic interactions. Surface diffusion is the sole rate-limiting step of l-Trp mass transfer on resin XDA-200. l-Trp was separated satisfactorily from l-glutamic acid (l-Glu) and NaCl with both the recovery rate and purity of l-Trp higher than 99% in the fixed bed packed with resin XDA-200.

Comments on "Fast and efficient removal of Cr(VI) to ppb level together with Cr(III) sequestration in water using layered double hydroxide interclated with diethyldithiocarbamate"

This paper primarily aimed to provide some concerns and continue discussion about the previous published paper in this journal. First, when the mechanism of Cr(VI) removal from solution involved in adsorption-coupled reduction was proposed, the X-ray photoelectron spectroscopy (XPS) of Cr 2p spectrum of laden adsorbent (i.e., DDTC-LDH after adsorption) needs to demonstrate the co-existence of Cr(VI) and Cr(III). The detection of reduced Cr(III) in solution after the completed adsorption of Cr(VI) only provides information on the mechanism regarding reduction, not adsorption-coupled reduction. Second, adsorption mechanism (chemisorption or physisorption) cannot be drawn only based on the best statistical fit between the time-dependent data of adsorption experiment and the kinetic model (i.e., the pseudo-second-order, Elovich, or Avrami model). Third, the constant K_RP (liters per grams of adsorbent not adsorbate; L/g) of the Redlich-Peterson isotherm model is not equal to or used as the thermodynamic equilibrium constant K_Eq^o. The application of the constant K_RP for calculating the thermodynamic parameters of adsorption process (∆G°, ∆H°, and ∆G°) using the van't Hoff equation leads to a certain error in the values (sign and magnitude) of those parameters. Fourth, the pH_PZC of adsorbent is significant different to its pH_IEP on both meanings and analysis methods. The use of those terminologies in the fields of material and sorption (adsorption and absorption) must be correct. Finally, some important information needs to provide in the studies of adsorption isotherm and mechanism (i.e., solution pH) and characteristics of diethyldithiocarbamate intercalated-LDH (i.e., arrangement and orientation of diethyldithiocarbamate in the interlayer region of DDTC-LDH).

Adsorption of methylene blue on sodium alginate-flax seed ash beads: Isotherm, kinetic and thermodynamic studies

In the present study, the adsorptive removal of methylene blue (MB) from wastewater was studied using the novel composite prepared by sodium alginate (SA) and flax seed ash (FS). The adsorption of MB was carried out using the composite beads consisting of different weight amounts of FS at different pH values and temperatures using different dye concentrations. The characterization studies of the composite beads were performed using Fourier-Transform infrared spectroscopy (FT-IR), scanning electron microscope (SEM), and Brunauer-Emmett-Teller and Barrett-Joyner-Hallenda (BET-BJH) analyses. BET and BJH surface area values of SA-FS adsorbent beads were found to be 45.01 m²/g and 14.35 m²/g, respectively. During the studies, it was determined that the adsorption percentage of MB reached the maximum with 90% at pH = 7 and 50 °C. Furthermore, Langmuir model fits well for the adsorption of MB using SA-FS with different FS ratios, SA, and FS adsorbents. The maximum adsorption capacity obtained from Langmuir model was found to be 333.3 mg/g for SA-FS-2 composite beads at pH = 7 and 50 °C. The adsorption kinetics were interpreted well by pseudo-second order model for SA, FS and SA-FS adsorbents. The calculated thermodynamic parameters indicated that MB adsorption by FS, SA, and SA-FS were spontaneous and an endothermic.

Removal of phenolic compounds from aqueous solution using MgCl2-impregnated activated carbons derived from olive husk: the effect of chemical structures

Activated carbon (BC) prepared from olive oil solid waste (olive husk) by slow pyrolysis was chemically activated using MgCl₂ (BC-MgCl₂). The BC and BC-MgCl₂ were used as adsorbents for removal of three phenolic compounds, namely, phenol (P), p-methoxyphenol (PMP) and p-nitrophenol (PNP), from aqueous solution. The uptake of these three phenolic compounds by the BC and BC-MgCl₂ was better expressed by the Langmuir and Dubinin-Radushkevich (D-R) isotherm models than by the Freundlich isotherm, and the kinetics of the adsorption process followed the pseudo-second order kinetic model. The maximum monolayer adsorption capacity of P, PMP and PNP were increased from 24.938, 45.455 and 61.728 on BC to 43.860, 98.039 and 121.951 mg/g on BC-MgCl₂ by factors of 1.76, 2.16 and 1.98, respectively. Therefore, the chemical activation of BC by MgCl₂ is indeed of importance for improving its adsorption performances. For both adsorbents, the adsorption phenomenon for different substituted phenols is a strong function of solubility, polarity, molecule structure, and size. At the tested temperatures (25, 35 and 45 °C), the negative values of ΔG° and positive values of ΔH° and ΔS° for the adsorption of P, PMP and PNP on BC and BC-MgCl₂ demonstrated that the adsorption was a spontaneous, endothermic and entropy-increasing process.