Exploration of the adsorption and desorption performance of volatile organic compounds by activated carbon with different shapes based on fixed-bed experiments.

Activated carbon (AC) has been widely used in volatile organic compounds (VOCs) treatment of industrial exhaust gases. Rather than modifying specific pore size distributions and surface properties, altering the shape of AC offers a more feasible approach to enhance its adsorption performance. This study investigates the adsorption-desorption performance of two different shaped ACs with highly similar properties for the removal of VOCs. The clover-shaped AC (CSAC) has a 27.46% lower internal void fraction and a 39.10% higher external void fraction compared to cylindrical AC (CAC), resulting in denser packing and longer contact time with VOCs. Adsorption experiments showed the CSAC has 40% longer adsorption breakthrough (BT) times for ethanol, ethyl acetate, and n-hexane on average, and 20% higher saturation adsorption capacity per unit volume. CSAC also has higher partition coefficients, with the highest values for ethanol, ethyl acetate, and n-hexane being 0.0187, 0.0382, and 0.0527 mol kg-1·Pa-1, respectively. The desorption process for selected VOCs is non-spontaneous and endothermic. Optimal desorption conditions were identified as an inlet space velocity of 3535 h-1, a desorption temperature of 150 °C, and a pulsed inlet method. To investigate the possibility of the application of CSAC in real-world scenarios, xylene was chosen as a representative industrial VOC. Results showed CSAC has 20% higher BT time and saturation adsorption capacity for xylene compared to CAC under different bed heights. The desorption efficiency for xylene on both ACs is below 40%. With increasing xylene inlet concentration, the mass transfer zone (MTZ) height initially increases but stabilizes beyond 1704 mg m-3. At identical bed heights, the MTZ height of CSAC is 29% shorter than CAC, indicating a higher bed utilization efficiency.

Preparation of carbon self-doped g-C3N4 for efficient degradation of bisphenol A under visible light irradiation.

In this study, visible-light-driven carbon self-doped graphitic carbon nitride photocatalyst was fabricated by a facile method with urea and ammonium citrate, and used for photodegradation of bisphenol A (BPA) in the aqueous environment. The experiments indicated that the prepared photocatalyst (C0.02CN) showed high catalytic activity, and 96.0%, 93.2%, and 95.5% BPA could be photodegraded in 150 min under pH 3, 6, and 11, respectively. The photocatalytic degradation rate (0.018 min-1) and mineralization (27.6%) of C0.02CN for BPA were about 6.7 and 3.5 times higher than those of the g-C3N4 (0.0027 min-1, 7.87%), respectively. C0.02CN had high reusability with a photodegradation efficiency of 84.5% for BPA after 3 cycles. Moreover, C0.02CN introduced additional carbon atoms, which generated C-O-C bonds in the g-C3N4 lattice. In contrast to g-C3N4, carbon doping enhanced the visible light absorption range of C0.02CN, reduced its band gap, and improved the separation efficiency of photogenerated electron-hole pairs. Radical quenching experiment and ESR results revealed that superoxide radicals (•O2-) and photogenerated holes (h+) acted as important parts in the high photodegradation activity under visible light irradiation. This work puts forward a one-pot strategy for the preparation of carbon self-doped g-C3N4, displacing the high-energy consuming and complicated preparation technology with promising industrial applications.

Effective adsorption of mercury by Zr(IV)-based metal-organic frameworks of UiO-66-NH2 from aqueous solution.

In this study, Zr-based metal-organic frameworks (MOFs) of UiO-66 and UiO-66-NH2 were synthesized and applied to removal of mercury from aqueous solution. The characterizations of UiO-66 and UiO-66-NH2 were examined by X-ray diffraction (XRD), scanning electron microscope (SEM), and thermogravimetric analysis (TGA). To investigate the adsorption properties of UiO-66-NH2 for mercury, the experiments of kinetics, isotherm, pH, temperature, and salt concentration were conducted, and the results were compared with those by UiO-66. The result showed that UiO-66-NH2 has a higher adsorption capacity for mercury than UiO-66. The maximum adsorption capacity of UiO-66-NH2 was 223.8 ± 17.8 mg g-1 at 313 K. The salt concentration of NaCl has a significant effect on the adsorption of mercury on UiO-66, while UiO-66-NH2 can maintain the stable adsorption capacity for mercury in the concentration range of 0.1-0.5 M NaCl. Adsorption thermodynamics result indicated that the adsorption process of mercury on UiO-66-NH2 was spontaneous and endothermic. Fourier transform infrared spectroscopy (FTIR) and X-ray photoelectron spectroscopy (XPS) analyses showed that the mercury was successfully adsorbed on the surface of UiO-66-NH2 and amino functional group as a soft base played a major role to react with mercury during the adsorption process. Graphical abstract.

Efficient removal of formaldehyde by polyethyleneimine modified activated carbon in a fixed bed.

Polyethyleneimine modified activated carbon (PEI-AC) was prepared through a treatment of immersion, and used for the adsorption of formaldehyde. The adsorption capacity of formaldehyde by unmodified AC is 190.1 mg g-1, and the adsorption capacity of formaldehyde can reach to 317.6 mg g-1 after 10 g L-1 of PEI modified, being about 1.67 times than unmodified activated carbon (AC: 191.2 mg g-1). And the 10 g L-1 of PEI modified AC (PAC-30) has the highest adsorption capacity of formaldehyde, reached to 650 mg g-1, with an increasing magnitude of 240% in comparison with that without modified AC. This is mainly due to changes in the pore structure and surface functional groups after modification. However, as the PEI concentration increases, the adsorption performance is inhibited. Through kinetic studies, it was found that all adsorption curves follow the second-order kinetics, and the breakthrough curves follow the Boltzmann model, and the adsorption process can also be described by the intraparticle diffusion model.

A novel strategy for Cr(VI) removal from aqueous solution via CYPH@IL101/chitosan capsule.

A novel adsorbent, chitosan capsule with filler of CYPH@IL101 (CYPH@IL101/chitosan capsule), was prepared using a summary process for the adsorption of Cr(VI) from aqueous solution. The effects of CYPH@IL101 content, pH, contact time, rotational speed and Cr(VI) concentration on the adsorption were studied. The results showed that the adsorption capacity of the chitosan capsule was benefit from the increase of CYPH@IL101 content. Besides, solution pH also played an important role in the adsorption process and the maximum adsorption capacity was achieved at pH 3. Kinetic studies suggested that the adsorption rate was controlled by the diffusion step at low rotational speed (50 r/min), but was controlled by chemical reaction at high rotational speed (150 and 250 r/min). Furthermore, the adsorption isotherms were studied by using Langmuir, Freundlich, BET, and Temkin models. The results demonstrated that the adsorption process fit Langmuir and TemKin models better, which indicated that the adsorption of Cr(VI) onto CYPH@IL101/chitosan capsule mainly depended on chemisorption and the active sites were uniformly distributed on the adsorbent surface. While, the maximum adsorption capacity obtained from Langmuir model was 104.38 mg/g. Finally, XPS and FTIR analyses revealed that Cr(VI) was adsorbed and then reduced to Cr(III) by CYPH@IL101/chitosan capsule.

Adsorptive removal of endocrine-disrupting compounds and a pharmaceutical using activated charcoal from aqueous solution: kinetics, equilibrium, and mechanism studies.

Bisphenol A (BPA), diethyl phthalate (DEP), and carbamazepine (CBZ) have been widely used in chemical and pharmaceutical fields, and their residues are detected in various environments. Therefore, to find a suitable method for removing the compounds from an aqueous solution, an adsorption method by granular activated charcoal (AC) was studied. To investigate the adsorption properties of AC, its kinetics, equilibrium, pH effects, and regeneration of AC were examined. Moreover, its surface properties (i.e., surface area, pore volume, functional groups, and surface charge) were characterized by N2 adsorption and desorption isotherm, Fourier transform infrared (FTIR), and zeta potential analyses. Experimental results show that AC has high removal efficiencies for the target compounds at the low initial concentration as well as high estimated adsorption capacities (qm) for DEP, BPA, and CBZ, whose values were 293.4 ± 18.8, 254.9 ± 16.2, and 153.3 ± 1.61 mg/g, respectively. In comparison with other adsorbents based on previously reported results, AC was shown to have generally higher removability for the three compounds than others. Moreover, it was observed that AC's ability to adsorb DEP and BPA was dependent on pH because of hydrolysis and ionization, respectively. Meanwhile, there is no pH effect for CBZ adsorption by AC. After 3 cycles of adsorption/desorption, AC still maintained 92, 100, and 82% of initial adsorption capacities for DEP, BPA, and CBZ, respectively. Therefore, the AC is an effective adsorbent for the removal of endocrine-disrupting chemicals and pharmaceuticals from aqueous solution.

Study on the copper(II)-doped MIL-101(Cr) and its performance in VOCs adsorption.

The metal-organic framework (MOF) materials, MIL-101(Cr), and copper-doped MIL-101(Cr) (Cu@MIL-101(Cr)) were prepared through hydrothermal method and were used to remove volatile organic compounds (VOCs) in this study. Morphological characterization demonstrated that MIL-101(Cr) and Cu-3@MIL-101(Cr) were octahedral crystal, with specific surface area of 3367 and 2518 m2/g, respectively. The results of XRD, TG, and FTIR showed that the copper doping procedure would not alter the skeleton structure, but it would affect the crystallinity and thermal stability of MIL-101(Cr). Besides, MIL-101(Cr) and Cu-3@MIL-101(Cr) displayed good removal efficiencies on benzene sorption, and the maximum sorption capacity was 103.4 and 114.4 mg/g, respectively. In competitive adsorptions, the order of adsorption priority on Cu-3@MIL-101(Cr) was as follows: ethylbenzene > toluene > benzene. Hence, it could be concluded that MIL-101(Cr) and copper-doped MIL-101(Cr) demonstrated good performance in VOCs adsorption and showed a promising potential for large-scale applications in the removal of VOCs. Graphical abstract ᅟ.

Adsorption of Ag (I) from aqueous solution by waste yeast: kinetic, equilibrium and mechanism studies.

One type of biosorbents, brewer fermentation industry waste yeast, was developed to adsorb the Ag (I) in aqueous solution. The result of FTIR analysis of waste yeast indicated that the ion exchange, chelating and reduction were the main binding mechanisms between the silver ions and the binding sites on the surface of the biomass. Furthermore, TEM, XRD and XPS results suggested that Ag(0) nanoparticles were deposited on the surface of yeast. The kinetic experiments revealed that sorption equilibrium could reach within 60 min, and the removal efficiency of Ag (I) could be still over 93 % when the initial concentration of Ag (I) was below 100 mg/L. Thermodynamic parameters of the adsorption process (ΔG, ΔH and ΔS) identified that the adsorption was a spontaneous and exothermic process. The waste yeast, playing a significant role in the adsorption of the silver ions, is useful to fast adsorb Ag (I) from low concentration.

Effect of functional groups on sludge for biosorption of reactive dyes.

The sludge, which was collected from a biological coke wastewater treatment plant, was used as a low-cost adsorbent in the removal of reactive dyes (Methylene Blue (MB) and Reactive Red 4 (RR4)) from aqueous solution. The pH of dye solution played an important role on the dye uptake. With the solution pH increase, the MB uptake increased; whereas the RR4 uptake decreased. The maximum uptake of RR4 by protonated sludge was 73.7 mg/g at pH 1, and the maximum uptake of MB by sludge was 235.3 mg/g at pH 9. Three functional groups, including carboxyl, phosphonate, and amine group, were identified by potentiometric titration, fourier transform infrared (FT-IR) spectrometry, and X-ray photoelectron spectroscopy (XPS). The anionic functional groups, phosphonate and carboxyl group, were identified as the binding sites for the cationic MB. Amine groups were identified to bind RR4. The main mechanism of the reactive dyestuffs adsorption is electrostatic interaction.

Adsorption performance and mechanism in binding of Reactive Red 4 by coke waste.

The protonated coke waste was used as a new type of adsorbent for the removal of Reactive Red 4. To identify the binding sites in the protonated coke waste, the waste was potentiometrically titrated. As a result, four types of functional groups were present in the waste, which was confirmed by FT-IR analysis. Among functional groups, primary amine groups (-NH2) were likely the binding sites for anionic Reactive Red 4. It was also found that sulfonate, carboxyl and phosphonate groups played a role in electrostatic interference with the binding of dye molecules. The maximum adsorption capacities of the coke waste were 70.3+/-11.1 and 24.9+/-1.8 mg/g at pH 1 and 2, respectively. Kinetic study showed a pseudo-first-order rate of adsorption with respect to the solution. The uptake of Reactive Red 4 was not significantly affected by the high concentration of salts. These results of adsorption performance indicate the coke waste as a potentially economical adsorbent for dye removal.