Removal of pentachlorophenol from aqueous solutions by dolomitic sorbents

Controlled synthesis of sulfhydryl-dendritic mesoporous silica nanospheres for ultrafast extraction and sensitive analysis of organochlorine herbicides containing amide groups

The distinctive morphology of dendritic mesoporous silica nanoparticles (DMSN) has recently attracted considerable attention in scientific community. However, synthesis of DMSN with well-defined structure and uniform size for ultrafast extraction of trace herbicide residues from environmental and food samples remains to be a compelling challenge. In this study, sulfhydryl functionalized dendritic mesoporous silica (SH-DMSN) was synthesized and the SH-DMSN showcases monodisperse microspheres with flower shape and precisely tailored and controllable pore sizes. This distinctive structural configuration accelerates mass transfer within the silica layer, resulting in heightened adsorption efficiencies. Furthermore, the particle sizes (455, 765, and 808) of the adsorbent can be meticulously fine-tuned by introducing distinct templates. Specifically, when the particle size is 765 nm, the optimized SH-DMSN exhibits a substantial specific surface area (691.32 m²/g), outstanding adsorption efficiencies (>90 %), remarkably swift adsorption and desorption kinetics (2 min and 3 min, respectively), and exceptional stability. The superior adsorption capabilities of this novel adsorbent, ranging from 481.65 to 1021.7 µg/g for organochlorine herbicides containing amide groups, can be attributed to the interplay of S-π interactions, halogen bonding, and electrostatic attraction interaction. These interactions involve the lone pair electrons of sulfhydryl and silanol groups with the π-electrons, halogen atoms and amide groups in herbicide molecules. This study not only offers a new perspective on advancing the practical utilization of dendritic mesoporous silica but also provides a pragmatic strategy for the separation and analysis of herbicides in diverse sample matrices.

Na4P2O7-Modified Biochar Derived from Sewage Sludge: Effective Cu(II)-Adsorption Removal from Aqueous Solution

With the rapid development of industrialization, the amount of copper-containing wastewater is increasing, thereby posing a threat to the aquatic ecological environment and human health. Sludge biochar has received extensive concern in recent years due to its advantages of low cost and sustainability for the treatment of heavy-metal-containing wastewater. However, the heavy-metal-adsorption capacity of sludge biochar is limited. This study prepared a sodium pyrophosphate- (Na4P2O7-) modified municipal sludge-based biochar (SP-SBC) and evaluated its adsorption performance for Cu(II). Results showed that SP-SBC had higher yield, ash content, pH, Na and P content, and surface roughness than original sewage sludge biochar (SBC). The Cu(II)-adsorption capacity of SP-SBC was 4.55 times than that of SBC at room temperature. For Cu(II) adsorption by SP-SBC, the kinetics and isotherms conformed to the pseudo-second-order model and the Langmuir–Freundlich model, respectively. The maximum adsorption capacity of SP-SBC was 38.49 mg·g−1 at 35°C. Cu(II) adsorption by SP-SBC primarily involved ion exchange, electrostatic attraction, and precipitation. The desired adsorption performance for Cu(II) in the fixed-bed column experiment indicated that SP-SBC can be reused and had good application potential to treat copper-containing wastewater. Overall, this study provided a desirable sorbent (SP-SBC) for Cu(II) removal, as well as a new simple chemical-modification method for SBC to enhance Cu(II)-adsorption capacity.

Optimization of the Pentachlorophenol Adsorption by Organo-Clays Based on Response Surface Methodology

The aim of this study is to optimize the adsorption of pentachlorophenol (PCP) using an organo-clay under the response surface methodology. The adsorbent was selected from a montmorillonite exchanged by various cations, such as Fe³⁺, Al³⁺, Zn²⁺, Mg²⁺, Na⁺, and modified by bromide cetyltrimethylammonium (CTAB) as surfactant. The obtained organo-montmorillonite was characterized using several techniques, such as Fourier-transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), thermogravimetric analysis (TGA), scanning electron microscopy (SEM), and nitrogen adsorption, performed at -196 °C. The results showed an increase in basal space from 1.65 to 1.88 nm and a decrease in the specific surface and pore volume, with an increase in pore diameter, including the presence of characteristic bands of -CH₂- and -CH₃- groups at 2926 and 2854 cm^-1 in the FTIR spectrum after the modification. The optimization of PCP removal by clay adsorbents is achieved using the response surface methodology (RSM) with a four-factor central composite model, including pH of solution, mass of adsorbent, contact time, and initial concentration. The results proved the validity of the regression model, wherein the adsorption capacity reaches its maximum value of 38 mg/g at a lower adsorbent mass of 20 mg, pH of 6, contact time (t_c) of 5 h, and initial concentration of 8 mg/L.

Combined first-principles calculations and experimental study on the photocatalytic mechanism of natural dolomite

Mineral-based photocatalysts have received great attention due to their low cost. In this study, the photocatalytic activity of natural dolomite and its mechanism were investigated based on designed experiments and first-principles calculations. The kinetic study showed that natural dolomite showed notable photocatalytic activity for the degradation of target compounds including methylene blue, diphenhydramine, and tetracycline. The EPR analysis demonstrated that O₂⁻˙, ˙OH, and ¹O₂ were produced in the dolomite system under simulated sunlight irradiation. The first-principles calculations indicated that the isomorphous substitution of Fe²⁺ for Mg²⁺ in the dolomite lattice led to the impurity levels appearing in the forbidden band, which caused a significant decrease of the band gap from 5.02 to 1.63 eV. As a result, natural dolomite could act as a semiconductor photocatalyst in photochemical reactions due to the substitution of Mg²⁺ by Fe²⁺. Under simulated sunlight irradiation, photogenerated electron–hole pairs in the natural dolomite were separated and transferred to the surface, and then formed reactive radicals through further reactions, thereby enhancing the degradation of target compounds. This research may contribute to the understanding of the photocatalytic activity of natural minerals.

Natural dolomite exhibits notable photocatalytic activity due to the isomorphous substitution of Fe²⁺ for Mg²⁺ in the lattice, implying that it can be used as a low-cost photocatalyst.

Efficient removal of pentachlorophenol from aqueous solution by 4-tert-butylcalix[8]arene modified thermally sensitive hydrogels

We prepared poly(N-isopropylacrylamide-co-4-tert-butylcalix[8]arene) (PNIPAM-TBCX) hydrogels by copolymerization of N-isopropylacrylamide (NIPAM) with 4-tert-butylcalix[8]arene (TBCX) to capture hazardous pentachlorophenol (PCP) from aqueous solution. Adsorption experiments showed that the adsorption capacities of PNIPAM-TBCX hydrogels reached 1.96, 2.08 and 2.02 mg PCP per 1 g of hydrogel, while the molar percentage ratio of TBCX in the hydrogels was as low as 0.5%, 0.7% and 1%. The equilibrium adsorption of PCP on the hydrogels was studied using different adsorption models. In addition, the PNIPAM-TBCX hydrogel still retained its performance when regenerated several times by immersing in water at 323 K.

We synthesized 4-tert-butylcalix[8]arene modified poly(N-isopropylacrylamide) hydrogels to enhance the adsorption ability for pentachlorophenol in aqueous solutions.

The kinetics of photocatalytic degradation of aliphatic carboxylic acids in an UV/TiO2 suspension system

Kinetic studies on the photocatalytic degradation of aliphatic carboxylic acids were carried out in a slurry photoreactor with in-situ monitoring, employing artificial UV light as the source of energy and nano-TiO2 powder as the catalyst. The influences on the photocatalytic degradation such as the initial concentration of reactant (C0), catalyst dosage (CTiO2), UV intensity (Ia) and pH value have been investigated. Good agreement has been obtained between the value calculated by Langmuir-Freundlich-Hinshelwood (L-F-H) model and experimental data, with coefficient of multiple determination (R2) varying from 0.880 to 0.999. The L-F-H model has been proven to be feasible in describing the kinetic characteristic of the photocatalytic degradation of aliphatic carboxylic acids. Moreover, the apparent reaction rate constant (k) of the photocatalytic degradation of dicarboxylic acids is higher than that of monocarboxylic acids with the same carbon atoms. This shows that the photocatalytic degradation rate is favoured by different chemical structure.

Functional Groups and Interactions Controlling the Adsorption of Bisphenol a onto Different Polymers

The behaviour of different polymers in the adsorption and removal of bisphenol A (BPA) from aqueous solutions was examined in order to identify the mechanism controlling the process. Three polymers with different functional groups were prepared and employed in our laboratory; they were characterized both texturally and chemically in terms of their surface areas, pore-size distributions, total exchange capacities and other parameters. The adsorption isotherms of bisphenol A were obtained and accurately modelled by the three-parameter Langmuir–Freundlich (LF) isotherm, the binding parameters calculated directly by the LF fitting coefficients indicating that increasing temperature was helpful in causing the adsorption process to move from positive cooperativity to negative cooperativity.

The kinetic data were found to be well represented by the pseudo-second-order kinetic model, indicating that the functional groups of the polymers had a significant influence on the adsorption mechanism of BPA. The adsorption of BPA basically depended on the chemical nature of the polymers and the pH value of the solution. The adsorption process was favoured by the molecular form of bisphenol A, since this controlled the surface complexes produced between the polymer surface and the bisphenol A molecules, with the resulting increase in adsorbent–adsorbate interactions being positively influenced by the temperature.

Sorption of pentachlorophenol on surficial sediments: the roles of metal oxides and organic materials with co-existed copper present

The sorption characteristics of pentachlorophenol (PCP) in the surficial sediments were investigated using a selective extraction procedure. The results show that the Gamma(max) of PCP sorption decreased from 1.60 micromol g(-1) to 0.69 micromol g(-1) by approximately 60% after selective removal of organic materials from the sediments. The sorption of PCP in the sediments after selective removal of Mn oxides increased nearly up to 600% (from 1.60 micromol g(-1) to 11.11 micromol g(-1)) and, to a less degree, the PCP sorption in the sediments after simultaneous removal of Fe/Mn oxides (Gamma(max)=3.53 micromol g(-1)). The analysis of the data using an additional model indicates that the contribution of Mn oxides to PCP sorption was negative, and Fe oxides and organic materials both have greater potential for sorption of PCP with less contribution from residues including Mn and Fe oxides in the residual fractions determined by a sequential extraction procedure and clay and silicate minerals. The differences in the decreased degrees of PCP sorption with increasing of Cu suggest that competition between Cu and PCP for sorption sites mainly takes place on Fe oxides.