Humic Acid Adsorption Process Research Articles

Evaluation of the efficiency of the TiO2 /UV nano-photocatalytic process in the removal of humic and fulvic acids from aqueous solutions

Background: Removing natural organic substances from drinking water sources is necessary to prevent the formation of toxic and carcinogenic disinfection by-products (DBPs). The nano-photocatalytic oxidation process to remove these substances is easier, faster, cheaper, and more efficient than other methods. Methods: This study investigated the efficiency of the TiO2 /UV nano-photocatalytic process in removing humic acid (HA) and fulvic acid (FA) from aqueous solutions. Batch tests were performed to investigate the effect of various parameters such as contact time (15, 30, 45, 60, and 75 minutes), initial pH (4, 7, and 9), initial HA and FA concentration (0.5, 1, 2, 5, and 7 mg/L-1), TiO2 dose (5, 10, 15 and 20 mg/L-1), and different UV irradiation (8 W and 16 W) for the removal of HA and FA from aqueous solutions using TiO2 /UV at room temperature (20±3 °C). The equilibrium adsorption data and the standard parameters were evaluated. Data were analyzed using SPSS version 25. Results: The efficiency of this process in optimal conditions (pH: 4, anatase TiO2 : 10 mg/L-1, irradiation time: 60 min, UV=16 W) for removing humic and fulvic (initial HA concentration: 2 mg/L-1 and initial FA concentration: 5 mg/L-1) was 89% and 92%, respectively. The analysis of the experimental isotherm data showed that in the adsorption process of HA and FA on TiO2 /UV, the Langmuir isotherm and the first-order reaction had the best fit with the experimental data. Conclusion: TiO2 /UV nano-photocatalytic process is suitable for the photo-degradation and removal of HA and FA in aqueous solutions.

Adsorptive removal of humic substances using cationic surfactant-modified nano pumice from water environment: Optimization, isotherm, kinetic and thermodynamic studies

In this study, nano pumice (NP) and a cationic surfactant (hexadecyltrimethylammonium-chloride (HDTMA.Cl)) treated nano pumice (HMNP) were used for humic acid (HA) adsorption from an aqueous solution. The adsorption process was modeled and optimized using Response surface methodology-central composite design (RSM-CCD) and Artificial neural networks- Genetic algorithm (ANN-GA). The results show that the ANN model outperforms the RSM-CCD model in terms of response prediction. Optimization results based on the RSM-CCD approach proposed pH 3, adsorbent dose 3 g L−1, reaction time 60 min, and initial HA concentration 5 mg L−1 as optimal points of the variables, to reach the maximum adsorption efficiency of 100% and 65.4% by HMNP and NP adsorbents. The maximal adsorption capacity of NP was 1.21 mg g−1, while that of HMNP was 27.34 mg g−1. The optimal points of process parameters by the ANN-GA method are in accordance with the values suggested by the RSM-CCD method. In isotherm studies, Langmuir model was found to be the best-fitted model for both adsorbent with R2 = 0.97 for NP and 0.992 for HMNP, and also among three different kinetic models which were assessed, Pseudo-second-order model with R2 = 0.9989 for HMNP and R2 = 0.9957 for NP were the best-fitted models for HA removal. Thermodynamic studies indicated that the HA adsorption process by both of the adsorbents is endothermic and the nature of HMNP was found spontaneous while for NP was non-spontaneous. The value of ΔH for both adsorbents was in the range of 34–36.8 kJ mol−1 so the process is clarified as chemical–physical adsorption. The reusability test revealed that the adsorption effectiveness of HMNP drops from 100% to 82.4% after 10 consecutive recycles. The influence of interfacing anions indicated that the adsorption efficiency drops from 100% to 95.4% when the anions were added to the reaction solution.

Adsorption behaviors and mechanisms of humic acid on virgin and aging microplastics

Because of the wide distribution and strong adsorption ability, microplastics (MPs) in aquatic environment tend to adsorb natural organic matter (NOM). This study aimed to investigate behaviors and underlying mechanisms of adsorption of humic acid (HA) on virgin and aging polyamide 66 (mPA66) and polypropylene (mPP). The kinetic data of HA adsorption on virgin and aging MPs well fitted the pseudo-second-order kinetics model (R2 > 0.95), while the adsorption isotherms better followed the Freundlich models (R2 > 0.92) than Langmuir models. The adsorption process of HA on the virgin and aging MPs was spontaneous and exothermic according to thermodynamics analysis. The effect of ionic strength on adsorption indicated that Ca2+ promoted more adsorption of HA on MPs than Na+ due to the formation of more cation bridge between Ca2+ and HA. With the pH increase, the adsorption capacity of HA first decreased and then increased. Desorption experiment showed that desorption efficiencies of HA adsorbed on virgin MPs were all relatively higher than those on corresponding aging MPs. Particularly, higher desorption efficiencies occurred in ultrapure water rather than in surface water, and HA desorption was apparently pH-dependent but slightly effect by ionic strength. Generally, HA had poor adsorption toward on virgin and aging MPs, but the following desorption efficiencies were relatively high, indicating that the adsorption of HA on virgin and aging mPA66 and mPP MPs tended to be reversible. This result was attributed to physical adsorption process, hydrophobic interactions, polarity and n-π electron donor-acceptor (EDA) interactions. The HA adsorption was mainly dominated by surface area of MPs, instead of crystallinity and functional groups based on XRD patterns, FTIR and XPS.

Effective Removal of Humic Acid by Zr-MOFs with Surface Modification

Humic acid (HA) in makeup water is one of the important safety issues of high-parameter power plants. Herein, the Zr-based metal organic frameworks (Zr-MOFs) were applied to remove humic acid in water. The mesoporous and active sites of Zr-MOFs were controlled by different ratios of ligands to increase the adsorption of HA. The maximum adsorption capacity was 150.15 mg g−1. The morphology and adsorption properties of the Zr-MOFs were characterized using scanning electron microscopy (SEM), X-ray diffraction (XRD), surface charge, Fourier Transform infrared (FT-IR), N2 adsorption-desorption and adsorption test. The adsorption process of HA accorded with the pseudo-second-order kinetics, while the adsorption isotherm conformed to the Langmuir model and the adsorption was proved to be a spontaneous and endothermic process. Physical adsorption by the mesoporous materials and the hydrogen bonding interactions between the Zr-MOFs and HA were the driving forces of HA adsorption. These results provided useful information for the effective removal of HA and enhanced our understanding of the adsorption mechanism of HA on Zr-MOFs.

Effective removal of humic acid by mesoporous Zr-MOF adjusted through SDBS.

Humic acid (HA) in makeup water is one of the important safety issues of high-parameter power plants. Herein, the Zr-based metal-organic frameworks (NH2-UiO-66) was applied to remove humic acid in water. The mesoporous of NH2-UiO-66 was controlled by surfactants sodium dodecyl benzene sulfonate (SDBS) to increase the adsorption of HA. The adsorption of HA at 25°C and pH 7 increased fast at the first 0.5 h and then gradually reached equilibrium after 10 h. The maximum adsorption capacity was 108.93 mg g-1, which removal efficiency was high as 95.0%. The morphology and adsorption properties of NH2-UiO-66 were characterized using scanning electron microscopy (SEM), X-ray diffraction (XRD), surface charge, Fourier transform infrared (FT-IR), N2 adsorption-desorption, and adsorption test. The adsorption process of HA accorded with the pseudo-second-order kinetics, while the adsorption isotherm conformed to be the Langmuir model and the adsorption was proved to be monolayer adsorption. Adsorption was the spontaneous and endothermic process (ΔG°<0, ΔH°>0). The accessible surface area provided by mesopores on the 5 different Zr-MOFs was the reason for the enhanced HA adsorption capacity. These results provided useful information for effective HA removing and enhanced our understanding of the adsorption mechanism of HA on NH2-UiO-66.

Simultaneous preparation of humic acid and mesoporous silica from municipal sludge and their adsorption properties for U(VI)

In this study, humic acid (HA) rich in various highly active functional groups was first synthesized by hydrothermal method using silica- and organic-rich municipal sludge, followed by mesoporous SiO2 with high specific surface area (SSA) by roasting. The prepared HA and mesoporous SiO2 were then used to adsorb uranium from an aqueous solution. The adsorption behaviors of two adsorbents were investigated using batch experiments, adsorption kinetic and isotherm models, and the adsorption mechanisms were analyzed by Fourier Transform Infrared Spectroscopy (FT-IR) and X-ray Photoelectron Spectroscopy (XPS). Under the present experimental conditions, the maximum adsorption capacity of HA was 220.26 mg/g. The adsorption process of HA was well described by the pseudo-second-order model and the adsorption isotherm was consistent with the Langmuir model. For mesoporous SiO2, the pseudo-second-order model and the Freundlich model better represent its adsorption behavior. Mechanism analysis showed that various functional groups such as amide, phenol, ether or alcohol on HA provide active sites for uranium adsorption, and mesoporous SiO2 has a porous structure and a large SSA, all of which play an important role in the uranium adsorption performance. By preparing two adsorbent materials from municipal sludge, not only the high-value utilization of sludge is fully realized, but also the environmental benefit is achieved through effective adsorption of uranium.

Investigating the role of the morphology of the Zn-Al LDH on the adsorption of humic acid from aqueous solutions.

Flake Zn-Al layered double hydroxides (FLDHs) and microspheres of LDH (MLDHs) were fabricated with a simple hydrothermal method to investigate the role of the morphology of Zn-Al LDH for humic acid (HA) adsorption from synthetic solutions and natural water. The effect of process variables, i.e. contact time, initial concentration of HA, pH, and competitive ions on the adsorption was investigated. HA removal mechanism was also studied. The two adsorbents exhibited different adsorption behaviors for HA in the presence and absence of background ions, which may be highly correlated with the various adsorption mechanisms involved. Comparison of the HA removal capacity of these two adsorbents implies the superior adsorption capability of FLDH for removal of HA from synthetic solutions (9.5 mg/g), while the adsorption capacity of MLDH was higher for natural organic matters present in natural water samples containing co-existing ions (8.9 mg/g). The pseudo-second-order kinetics model and Longmuir isotherm model could adequately interpret the HA adsorption process for the studied adsorbents. Both LDHs exhibited good regeneration and recycling abilities.

Synthesis of Mg/Al-LDH nanoflakes decorated magnetic mesoporous MCM-41 and its application in humic acid adsorption

In this study, Mg/Al-LDH nanoflakes decorated magnetic mesoporous MCM-41 (magMCM-LDH) was prepared, and the materials were used as an adsorbent for the removal of humic acid (HA) from aqueous solution. The preparation, morphology, composition and magnetic properties of magMCM-LDH were characterized by various techniques. The results suggested that the Mg/Al-LDH nanoflakes have successfully decorated on the magMCM-41. Various batch experiments were conducted to investigate the influence of contacting time, initial concentration, solution pH and ions concentration. The results suggested that the adsorption process of HA onto 10-magMCM-LDH was spontaneous and endothermic, which conformed to the pseudo-second-order and Langmuir isotherm models. The maximum adsorption capacity of 10-magMCM-LDH was 181.14 mg/g at the temperature of 298 K. A lower pH and a higher ion concentration of the solution can be beneficial to the adsorption process. The adsorbent processed an excellent practical application and regeneration ability. Finally, FT-IR, XRD, XPS analyses proved that the electrostatic interactions and ion-exchange may play an important role in the adsorption process.

Efficiency of Zeolite Coated with Zero-Valent Iron Nanoparticles for Removal of Humic Acid from Aqueous Solutions

The most important effect of natural organic materials in water is reacting with disinfectants and creating disinfectant by-products that are mostly carcinogenic. The aim of this study was to determine the optimum conditions for removal of humic acid (HA) by zeolite coated with nZVI nanoparticles (Zeolite/nZVI) from aqueous solutions. In this study, after synthesis of zeolite/nZVI, its structure and morphology were examined using FTIR, BET, XRF, and FESEM techniques. The effects of HA concentration, composite content, pH, and reaction time were evaluated. The experimental data were analyzed by Langmuir and Freundlich isotherm and pseudo-first-order and second-order kinetic models. Finally, the thermodynamic parameters of enthalpy (ΔΗ°), entropy (ΔS°), and Gibbs free energy (ΔG°) were calculated. The results of the analyses confirmed the accuracy of the composite structure. Its specific surface area by using BET method was 203.43 m2/g. The HA removal efficiency was obtained at 92.98% in optimum conditions of 50 mg/L concentration, 2 g/L composite dose, pH = 3, and reaction time of 60 min. The results of the isotherm and kinetic study showed that the HA adsorption process follows the Langmuir isotherm (R2 = 0.9707) and pseudo-second-order kinetic. The maximum adsorption capacity of the composite was determined at 23.36 mg/g by Langmuir model. Thermodynamic parameters indicate that the adsorption of HA endothermic and the reaction cannot be done spontaneously. Zeolite/nZVI composite had good removal efficiency after five times of recycling. The present study showed that zeolite/nZVI can be used as an effective adsorbent for removal of HA from aqueous solutions.

Study of Humic Acid Adsorption Character on Natural Maifan Stone: Characterization, Kinetics, Adsorption Isotherm, and Thermodynamics.

In this paper, the adsorption of humic acid (HA) on natural maifan stone (MS) in aqueous medium was investigated. The changes in MS after adsorption have been characterized explicitly. The adsorption behavior was studied by varying the factors of pH (5–10), reaction time (10–180 min), initial HA concentration (5–50 mg/L), adsorbent dosage (0.1–1.2 g), and temperature (25–45 °C). The kinetics of the adsorption process of HA was fitted well with the pseudo-second-order model (R2 = 0.99). The isothermal results revealed that the adsorption process is favorable, and highly fitting Langmuir models (R2 > 0.99) were used. Additionally, the obtained maximum adsorption capacity of MS for HA was approximately 1 mg/g. The adsorption process of HA onto MS was endothermic according to the thermodynamic study. The changes in the excitation–emission–matrix of HA and the X-ray diffraction of MS after adsorption indicate the interaction of HA and MS. However, the reason for these changes is still unclear. Thus, the results show that the natural MS exhibited a certain adsorption capacity for HA. It is promising to develop novel natural MS-based materials for adsorption of HA.

A comparative study of using barberry stem powder and ash as adsorbents for adsorption of humic acid.

In the present research, investigation of the practical utility of barberry stem powder (BSP) and barberry stem ash (BSA) for humic acid (HA) removal from an aqueous medium by adsorption was carried out. The adsorption process was tested by varying of pH (3-11), reaction time (5-20 min), initial HA concentration (5-40 mg/L), adsorbent dosage (1-4 g/L), and temperature (15-35 °C). The isothermal results revealed that the adsorption process is favorable for both used adsorbents and it is highly described using the Freundlich and Langmuir models (R2 > 0.960). Also, the maximum uptakes of BSP and BSA for HA were 20.220 and 16.950 mg/g at the abovementioned optimized conditions (pH = 7, reaction time = 10 min, temperature = 15 °C, initial HA concentration = 40 mg/L, and adsorbent amount = 1.0 g/L), respectively. The results achieved from the fitting of the experimental data with Dubinin-Radushkevich isotherm model showed that the HA molecules are adsorbed onto the BSP and BSA by physiosorption process. From the thermodynamic study, it appeared that the biosorption process of the HA onto two studied adsorbents was of exothermic nature. The kinetics of the adsorption process of HA has been found to be pseudo-second-order model (R2 = 0.930-0.999). Thus, the results obtained from this paper elucidated that the BSP exhibited higher adsorption capacity in comparison to BSA, for HA removal up to permissible concentrations.

Adsorption of Humic Acid from Aqueous Solution onto PAA Nanofiber: Thermodynamic Study

The potential of polyacrylic acid (PAA) nanofiber prepared by the electrospinning technique for the humic acid (HA) adsorption from aqueous solution was investigated. In this study, the adsorption experiments were carried out to investigate the effect of temperatures in a batch system. From experiment it can be seen that the HA adsorption using PAA nanofiber increased with increasing temperature. Thermodynamic parameters data indicated that the HA adsorption process was non-spontaneous and endothermic under the experimental conditions, with the Gibbs free energy (∆Go) in the range of 1.721-0.980 kJ mol-1, enthalpy (∆Ho) and entropy (∆So) of 7.24 kJ mol-1 and 18.52 J mol-1 K-1, respectively.

Effect of modification by five different acids on pumice stone as natural and low-cost adsorbent for removal of humic acid from aqueous solutions ‐ Application of response surface methodology

Pumice stone is a natural, low-cost, available adsorbent. This study aimed to investigate the efficacy of modified pumice with five different acids (acetic acid, hydrochloric acid, phosphoric acid, sulfuric acid, and nitric acid) for the removal of humic acid (HA) from aqueous solutions. Four variables were investigated: adsorbent dose (1–7 g/L), contact time (15–75 min), initial concentration (5–25 mg/L), and pH (3−11) by response surface methodology (RSM) and lab experiments. Results revealed that the amount of humic acid removal by the raw and modified adsorbents was increased by increasing the adsorbent dosage and contact time, whereas, in terms of initial concentration and pH variables, the opposite was observed. The pH and initial HA concentration had the maximum and minimum effects on the adsorption process, in all used acids, respectively. For all the adsorbents, the optimum efficiency was achieved in the following conditions: contact time = 75 min, pH = 3, pumice dosage = 7 g/L, HA initial concentration = 5 mg/L.Additionally, it was seen that the pumice modification could considerably increase the adsorbent efficiency. The comparative effectiveness of acids on the pumice adsorbent was in the order of H2SO4 > HNO3 > H3PO4 > HCOOH> HCl. Furthermore, the data fitting using different isotherm models and adsorption kinetics specified that the data were following Langmuir and Freundlich isotherms and pseudo-second-order kinetics. The data fitting using D-R isotherm similarly revealed that the HA adsorption process was physical on all the adsorbents. This study demonstrated that the acid-modified pumice could be utilized as an economic, naturally available adsorbent for the HA removal.

Removal of humic acid from aqueous solution using polyacrylamide/chitosan semi-IPN hydrogel.

In this study, we provide the first documented removal of humic acid (HA) from aqueous solution using polyacrylamide/chitosan (PAAm/CS) semi-IPN hydrogel. The prepared semi-IPN hydrogel was characterized by scanning electron microscopy (SEM) and Fourier transform infrared spectroscopy (FT-IR). The factors effecting HA adsorption performance were individually tested, including initial pH, ionic strength, contact time, initial HA concentration, and temperature. The results indicated that semi-IPN hydrogel was successfully fabricated and can be applied in a wide pH range, from 3 to 9. Low ionic strength effectively enhanced the adsorption capacity. As the ionic strength increased, this enhancement was less obvious but still positive. The adsorption kinetics were fitted to a pseudo-first-order kinetic model, and the adsorption isotherm was described using the Sips isotherm model. The HA adsorption capacity increased with increasing temperature. The maximum adsorption capacity has the potential to attain 166.30 mg g-1, based on the Sips isotherm at 25 °C. Experiments demonstrated that the HA adsorption process can be primarily attributed to electrostatic interactions, and hydrogen bonding was also involved. Facile synthesis and good adsorptive performance indicate that semi-IPN hydrogel can be used for removing HA from water.

Silica-coated magnetite nanoparticles core-shell spheres (Fe3O4@SiO2) for natural organic matter removal.

BackgroundIn this work, the magnetite (Fe3O4) nanoparticles (MNPs) and silica-coated magnetite nanoparticles (SMNPs) were synthesized as adsorbents for removing humic acid (HA) from water resources.MethodsThe adsorption processes were performed in batch experiments with which the influence of pH, reaction time, adsorbent dosage, initial concentrations of HA and temperature were investigated. Specific techniques were applied to characterize the features of both adsorbents (i. e. TECHNIQUES) (SEM, XRD, TEM, BET, EDX and VSM).ResultsThe maximum saturation magnetization for SMNPs was 30.2 emu/g, which made its separation from the solution by a magnetic field to be easier and faster. The HA adsorption process onto the both adsorbents were best described by the Freundlich isotherm and pseudo-second-order kinetic models. Highest adsorption efficiency of HA by MNPs an d SMNPs occurred at acidic conditions (pH ≈ 3). The mechanisms of adsorption process involved with a physisorption process such as (i. e. hydrogen bonding and electrostatic interaction). The predicted maximum monolayer adsorption capacities obtained by Langmuir isotherm model for MNPs and SMNPs were 96.15 and 196.07 mg/g, respectively.ConclusionHigher amount of HA adsorption onto the surfaces of SMNPs than MNPs surfaces was observed, reflecting that silica impregnated on MNPs enhances the efficiency of the adsorbent in removing HA.Electronic supplementary materialThe online version of this article (doi:10.1186/s40201-016-0262-y) contains supplementary material, which is available to authorized users.

Preparation of Fe3O4-chitosan hybrid nano-particles used for humic acid adsorption

The adsorbent of Fe3O4-chitosan hybrid nano-particles have been prepared. In this process, these materials were initially synthesized by chemical co-precipitation and then cross-linked with chitosan to coat on the surface of Fe3O4 nano-particles. The characterization of the synthesized Fe3O4-chitosan hybrid nano-particles was performed using FTIR, XRD, TEM, EDX, BET and TGA. Finally, the Fe3O4-chitosan hybrid nano-particles were used for the adsorption of humic acid (HA) from aqueous solutions using batch adsorption technique. The influences of contact time, pH, adsorbent dosages, initial concentration of HA and temperatures on the adsorption process were studied. The adsorption isotherms were better fitted by Langmuir isotherm with the adsorption capacity was found to be 44.84mg/g. The results of the kinetic study showed that the adsorption of HA onto Fe3O4-chitosan hybrid nano-particles could be described by the pseudo second order kinetic model with a rate constant in the range of 0.032–0.104gmg−1min−1, respectively. Thermodynamic parameters data indicated that the HA adsorption process was non spontaneous and endothermic under the experimental conditions, with the values of Gibbs free energy (ΔGo) were in the range of 2.92–4.65kJ/mol; as well as the values of enthalpy (ΔHo), entropy (ΔSo) and the activation energy (Ea) were found to be 21.80kJ/mol, 57.55J/mol and 19.27kJ/mol, respectively. The computational chemistry study showed that the interaction between adsorbent and HA was occurred through the interaction between amine groups of chitosan and phenol groups of HA. The adsorption of HA from real sample using the prepared adsorbents showed that the Fe3O4-chitosan hybrid nano-particles has higher adsorption percentages than both Fe3O4 nano-particles and pure chitosan.

Competitive adsorption of 2,4-dichlorophenoxyacetic acid herbicide and humic acid onto activated carbon for agricultural water management

Adsorptive removal of herbicide 2,4-dichlorophenoxyacetic acid (2,4-D) and humic acid (HA) from their single- and binary solutions was investigated using powdered activated carbon. Both pore- and film diffusion coefficients for 2,4-D calculated based on two resistance diffusion kinetics were higher than those found for HA both single- and binary component systems. Similar trend was also observed for the rate constants calculated by applying pseudo-second-order kinetic model. The L-shaped isotherm curves converted into H shaped with an increase in the temperature from 288 to 318 K indicating the complete removal of both solutes in dilute solutions. A synergetic effect was observed in low-concentration region in binary systems; however, the combined action of 2,4-D and HA was found to be antagonistic in concentrated solutions. The experimental equilibrium results in single-component systems were better predicted by the Freundlich than the Langmuir isotherm equation. The extended Freundlich isotherm model fit also quite well to the data obtained from binary solutions. The effects of medium acidity and salinity on 2,4-D and HA adsorption process were also examined. Analysis of the pH-dependent adsorption results using Kurbatov approximation suggested that 2,4-D and HA were mainly adsorbed in molecular form on carbon surfaces rather than in their anionic forms.

Fe3O4 nano-particles prepared by co-precipitation method using local sands as a raw material and their application for humic acid removal

Magnetic Fe3O4 nano-particles were prepared successfully from commonplace sands as a raw material. The nano-particles were synthesized by chemical co-precipitation of high purity iron separated from commonplace sands through acidic leaching. The characterization of the synthesized nano-particles was performed using X-ray diffraction, fourier transform infrared, scanning electron microscopy, transmission electron microscopy, and potential zeta. Finally, the nano-particles were used for adsorption of humic acid (HA) from aqueous solutions using batch adsorption technique. The effects of pH, adsorbent dosage, agitation time, initial HA concentration, and temperatures on HA adsorption were evaluated. The adsorption of HA onto nano-particles followed the Sips isotherm and pseudo-second order kinetics models. Thermodynamic parameters data indicated that the HA adsorption process was non-spontaneous and endothermic under the experimental conditions. The adsorption of HA from peat water (the real sample) using the nano-particles demonstrated that they were an adsorbent with great potential for the removal of HA from peat water.

Molecularly imprinted polymers (MIPs): a functional material for removal of humic acid from peat water

The aim of this study is to investigate the use of moleculary imprinted polymers (MIPs) material as an alternative adsorbent for the adsorption of humic acid (HA) from peat water in batch mode. The MIPs were prepared with methyl methacrylate as a monomer, HA as templates, ethylene glycoldimethacrylate as a cross-linker, and dimethyl formamide as a solvent. The characteristics of MIPs were evaluated using Fourier transform infra-red spectroscopy, scanning electron microscope, and Brunauer–Emmett–Teller methods. The Langmuir, Freundlich, and Sips models were applied to describe the equilibrium isotherms using non-linear regression analysis. Pseudo-first-order, pseudo-second-order, intraparticles, and Boyd kinetic models were used to describe the kinetic data. The results showed that the equilibrium contact time was 60 min. The experimental results indicated that the percentage of sorption increases with an increase in the adsorbent dosage and temperature. The adsorption percentage decreased with increasing peat water pH from 2 to 12. The equilibrium data fitted well for the Langmuir adsorption isotherms, with monolayer adsorption capacity of MIPs found to be 45.45 mg/g. The results of the kinetic study show that the adsorption of HA onto MIPs could be described by the pseudo-second-order kinetic model with a rate constant in the range of 0.034–0.115 g/mg min and controlled by film diffusion, with the effective diffusion coefficient was found in the range of 7.42 × 10−8–13.84 × 10−8 cm2/s. Thermodynamic parameters data indicated that under the experimental conditions, the HA adsorption process was non-spontaneous and endothermic, with the Gibbs free energy (∆G°) in the range of 3.71–1.17 kJ/mol, whereas enthalpy (∆H°) and entropy (∆S°) at 16.17 and 42.70 J mol−1, respectively.

Two-dimensional correlation spectroscopic analysis on the interaction between humic acids and TiO2 nanoparticles.

The elucidation of the interaction between TiO2 nanoparticles (NPs) and natural organic matter (NOM) can help one to better understand the fates, features, and environmental impacts of NPs. In this work, two-dimensional (2D) Fourier transformation infrared (FTIR) correlation spectroscopy (CoS) assisted by the fluorescence excitation-emission matrix (EEM) method is used to explore the interaction mechanism of humic acid (HA) with TiO2 NPs at a molecular level. The results show that the C═O bonds (carboxylate, amide, quinone, or ketone) and C-O bonds (phenol, aliphatic C-OH, and polysaccharide) of HA play important roles in their interaction with TiO2 NPs. The adsorption process of HA onto the surface of TiO2 NPs is different from the bonding process of the two species in solution. The forms of the relevant groups of HA and their consequent reaction with TiO2 NPs are affected to a great extent by the solution pH and the surface charge of NPs. The 2D-FTIR-CoS method is found to be able to construct a comprehensive picture about the NOM-TiO2 NPs interaction process. This 2D-FTIR-CoS approach might also be used to probe other complicated interaction processes in natural and engineered environments.