Green synthesis of ZnO nanoparticles and comparison of 2,4-dinitrophenol removal efficiency using photocatalytic, sonocatalytic, and adsorption processes

In the present work, the extract of a paper-flower species called Bougainvillea spectabilis was used to green synthesis of ZnO nanoparticles (NPs). The synthesized ZnO NPs was confirmed by XRD, SEM, TEM, EDS, and FTIR techniques. Then, the ability of ZnO NPs to remove 2,4-dinitrophenol from aqueous solutions was investigated using photocatalytic and sonocatalytic processes. All experiments were carried out in a batch system and the effects of pH, NPs dosage, concentration, and contact time were evaluated. The findings of this study showed that the pseudo-second-order kinetic model could well describe the removal of 2,4-dinitrophenol by ZnO NPs. Langmuir, Freundlich, Temkin, and BE-T isotherm models were also assessed in a dark condition. The Freundlich isotherm model was able to provide the best fit with the experimental data. Examination of the results showed that the degradation of 2,4-dinitrophenol at the presence of ultraviolet (UV) and ultrasonic (US) waves was able to increase the removal efficiency to about twice as much as removal by adsorption alone. Also, The obtained results showed that the maximum removal of 2,4-dinitrophenol under photocatalytic and sonocatalytic conditions occurred at the presence of 25 mg of NPs, solution pH of 4, and 2,4-dinitrophenol concentration of 20 ppm. The best rates of photocatalytic and sonocatalytic degradation under the optimal conditions were 84.42% and 77.13% during 60 min, respectively. Thermodynamic studies indicated that the degradation of 2,4-dinitrophenol by ZnO NPs is a spontaneous and endothermic process in the direction of increasing entropy. The zinc oxide NPs have better performance in the removal of 2,4-dinitrophenol at the presence of UV and US waves.

Rapid Adsorption Removal of Triclosan and p-chloro-m-xylenol In Water By Nitrogen Doped Magnetic Porous Carbon

Contamination of water resources with organic substances like phenolic fungicides is undesirable due to the improvement of living standards, huge production and consumption of daily chemicals, and an increase in the population. In this study, ZIF-67(Co) was synthesized using the “one pot method”, and the Co-magnetic porous carbon (Co-NPC) was prepared by ZIF-67 (Co) carbonization in an atmosphere of N2. The materials were tested using a X-ray diffractometer (XRD), scanning electron microscope (SEM), infrared spectroscopy (IR), Raman spectroscopy, X-ray photoelectron spectroscopy (XPS), N2 adsorption-desorption and magnetization analysis. These methods indicated that the Co-NPC was successfully prepared. With the original morphology of ZIF-67 (Co) crystal, the Co-NPC also has good porosity, magnetic properties and a large specific surface area. In water, Co-NPC-800 has a good adsorption capacity for triclosan (TCS) and p-chloro-m-xylenol (PCMX), which are kinds of aromatic fungicides. The adsorption of Co-NPC-800 on both reached equilibrium within 3 min, which is in accordance with the quasi-second-order kinetic model. At 298 K, the maximum adsorption capacity of Co-NPC-800 for TCS and PCMX was 163 and 39 mg·g-1, respectively. The adsorption of TCS and PCMX by Co-NPC-800 is a spontaneous endothermic process with reduced entropy. The combination of Co-NPC-800 and phenols come from multiple action of electrostatic, π-π and hydrogen bond effects. Moreover, Co-NPC-800 can be regenerated through simple washing and can be reused several times. Therefore, Co-NPC-800 has great potential to be applied across sewage treatments and other environmental fields.

Adsorption of benzalkonium chlorides onto powdered activated carbon: mechanisms and detoxification

Because disinfectants have been essential during the COVID-19 pandemic, the global demand for benzalkonium chlorides (BACs) has significantly increased. BACs can inactivate coronaviruses, but are known as toxic. In this study, we investigated the adsorption mechanisms of BAC12, BAC14, and BAC16 in water using powdered activated carbon (PAC). The effects of the reaction time, pH, and temperature on the adsorption kinetics of BACs were examined. The adsorption reaction followed pseudo-second-order kinetics, and better fitted to the Langmuir isotherm than the Freundlich isotherm. The best adsorption of BACs was achieved at neutral pH conditions. Thermodynamic analysis revealed that adsorption of BACs onto PAC is a spontaneous and endothermic process. Competitive adsorption experiments revealed that BACs with longer alkyl chains were adsorbed more effectively onto PAC than shorter alkyl chain BACs, implying that, while the electrostatic interaction is an important adsorption mechanism for BAC12, van der Waals interaction plays a more important role during the adsorption of BAC14 and BAC16. Finally, we observed the partial detoxification (69%) BAC in adsorption treated water with PAC using a Microtox test.

Equilibrium, Kinetic, and Thermodynamic Studies of Cationic Dyes Adsorption on Corn Stalks Modified by Citric Acid

The modification of agricultural wastes and their use as low-cost and efficient adsorbents is a prospective pathway that helps diminish waste and decrease environmental problems. In the present research, the natural adsorption capacity of corn stalks (CS) was improved by modification of their surface with citric acid. The adsorption capacity of the modified corn stalks (CS-C) was determined with the help of cationic dyes (methylene blue and malachite green). The equilibrium, kinetics, and thermodynamics of the cationic dyes on CS-C were studied. The Langmuir isotherm model best fitted the data both for methylene blue and malachite green adsorption on CS-C. The adsorption kinetics of the cationic dyes was well described by the pseudo-second order model. Thermodynamic studies revealed that adsorption of the cationic dyes on CS-C was an endothermic process. Negative results of ΔGo (between −31.8 and −26.3 kJ mol−1) indicated that the adsorption process was spontaneous in all the tested temperatures. The present study verified that citric acid-modified corn stalks can be used as a low-cost and effective adsorbent for removal of cationic dyes from aqueous solutions.

Structure Control of Novel Hierarchical Porous Carbon Material and its Adsorption Properties

Novel hierarchical porous carbon materials (HPCs) were fabricated via a reactive template-induced in situ hypercrosslinking procedure. The effects of carbonization conditions on the microstructure and morphology of HPC were investigated, and the adsorption of methylene blue (MB) on HPC was explored. The as-prepared HPC has a hierarchical micro-, meso- and macropore structure, which results from the overlap of hollow nanospheres possessing microporous shells and macroporous cavities. The carbonization temperature, carbonization time and carbonization heating rate played important roles in tailoring the nanostructures of HPC. The BET specific surface area and micropore specific surface area can reach 2388 m2·g−1 and 1892 m2·g−1, respectively. Benefitting from the well-developed pore structure, the MB removal efficiency can reach 99% under optimized conditions. The adsorption kinetics and thermodynamics can be well described by a pseudo-second-order model and Langmuir model, respectively. Furthermore, such adsorption is characterized by a spontaneous endothermic process.

Phosphorus and sulphates removal from wastewater using copper smelter slag washed with acid

In this study, we present the performance of acid washed copper smelter slag for the adsorption of phosphates and sulphates from wastewater. The aim of the study was to investigate the removal of phosphates and sulphates from wastewater using acid washed copper smelter slag at batch scale by exploring influences of different variables. The leachate concentrations of copper, iron, manganese and lead released from the adsorbent were 1.8, 128.2, 0.32 and 0.20 mg L−1, respectively at pH 2. The point of zero charge was at pH 6.04, Pseudo-Second Order kinetic model described the adsorption process better with an R2 value of 0.99. The experimental maximum adsorption capacities for phosphates and sulphates were 0.51 and 0.24 mg g−1 media, respectively, and 0.96 mg P g−1 media at pH 12 and 0.39 mg g−1 media for sulphates at pH 2, respectively. The process was endothermic with temperature having insignificant impact during adsorption. The maximum adsorption capacities for thermodynamic study were 0.103 ± 0.09 and 0.046 ± 0.004 mg g−1 media respectively, for PO43− P and SO42− at 60 °C. This study showed that acid washed copper smelter slag has an improved adsorption capacity for phosphate and sulphate ions but further investigations should be conducted to find ways of further improving the adsorbent performance. Article highlights There is increase in the adsorption capacity of acid washed copper smelter slag. The adsorption capacity of phosphorus is high at pH 12 and for sulphate at pH 6. The adsorption of phosphate and sulphate ions onto acid washed slag is an endothermic process. Intraparticle diffusion was not the only rate controlling mechanisms.

Re-utilization of Chinese medicinal herbal residue: waste wormwood rod-derived porous carbon as a low-cost adsorbent for methyl orange removal

A cost-effective approach was applied to prepare porous carbon samples by the simple carbonization of wormwood rod followed by salt activator (NaCl) activation. The effect of preparation parameters on the characteristics of the wormwood rod based porous carbons (WWRs) were studied. The properties of these samples were investigated by SEM, BET surface area, X-ray diffraction, FT-IR spectra and X-ray photoelectron spectrometer. The prepared WWRs were applied as new adsorbent materials to remove methyl orange (MO). The experimental results indicated that WWR-800 activated at 800 °C possesses the best adsorption performance. Several factors that affected the adsorption property of the system such as the solution pH, dosing of adsorbent, initial dye concentration and ionic strength were examined. In addition, the thermodynamic parameters and kinetic parameters of MO with WWR-800 were studied. The results indicated that the adsorption of MO on WWR-800 was an endothermic process and non-spontaneity under standard conditions. The maximum equilibrium adsorption capacity of MO on WWR-800 was 454.55 mg/g. After five adsorption/desorption cycles, the adsorption capacity of MO on WWR-800 remained at 94%, which indicated that wormwood rod based porous carbon possessed good reusability.

Highly efficient scavenging of Cr(VI) by two-dimensional titanium carbide nanosheets: kinetics, isotherms and thermodynamics analysis

In this study, two-dimensional (2D) MXene material (Ti3C2Tx) was employed to investigate its potentials toward the Cr(VI) removal in aqueous system by batch experiments. Characterization techniques such as SEM-EDS, HRTEM, XRD, FI-TR and XPS were used to analyze the structure and interaction of Ti3C2Tx before and after Cr(VI) adsorption. The results indicated that layered structure of Ti3C2Tx had unique surface functional properties and abundant active sites, such as –OH, Ti–O, C = O, which exhibited high adsorption capacity for the Cr(VI) removal. The Cr(VI) adsorption capacity by Ti3C2Tx decreased with the increase of pH, and its maximum value can reach 169.8 mg/g at pH = 2.0. The adsorption kinetic was well-explained by a pseudo-second-order kinetic, indicating that chemical interaction played a dominant role in the adsorption of Cr(VI) on Ti3C2Tx. Meanwhile, the isotherm data was calculated to conform the Freundlich isotherm model. Thermodynamic analysis indicated that the adsorption process of Cr(VI) on Ti3C2Tx was a spontaneous endothermic process. These experimental results revealed that Ti3C2Tx had tremendous potential in heavy metals adsorption from aqueous solutions.

Ni/Cr-[α-SiW12O40] Layered Double Hydroxide as Effective Adsorbent of Iron(II) From Aqueous Solution

Layered double hydroxide (LDH) Ni/Cr intercalated [α-SiW12O40]4- has been prepared using the coprecipitation method. Materials were characterized by X-ray, FTIR, BET, and pHpzc analyses. Material Ni/Cr-[α-SiW12O40] LDHs exhibited a high surface area 98.986 m2 g-1 from 11.030 m2 g-1 for Ni/Cr LDH where the interlayer space was an increase from 7.99 to 10.87 Å with indicated that high crystallinity. Ni/Cr-[α-SiW12O40] LDHs showed higher adsorption capacity for iron(II) is up to 250 mg g-1. Adsorption of iron(II) on LDHs has an endothermic process and classify as physical adsorption.

Fabrication of attapulgite/magnetic aminated chitosan composite as efficient and reusable adsorbent for Cr (VI) ions

An efficient composite was constructed based on aminated chitosan (NH2Cs), attapulgite (ATP) clay and magnetic Fe3O4 for adsorptive removal of Cr(VI) ions. The as-fabricated ATP@Fe3O4-NH2Cs composite was characterized by Fourier Transform Infrared Spectroscopy (FTIR), Thermal Gravimetric Analyzer (TGA), Scanning Electron Microscope (SEM), Zeta potential (ZP), Vibrating Sample Magnetometer (VSM), Brunauer–Emmett–Teller method (BET) and X-ray photoelectron spectroscope (XPS). A significant improve in the adsorption profile was established at pH 2 in the order of ATP@Fe3O4-NH2Cs(1:3) > ATP@Fe3O4-NH2Cs(1:1) > ATP@Fe3O4-NH2Cs(3:1) > Fe3O4-NH2Cs > ATP. The maximum removal (%) of Cr(VI) exceeded 94% within a short equilibrium time of 60 min. The adsorption process obeyed the pseudo 2nd order and followed the Langmuir isotherm model with a maximum monolayer adsorption capacity of 294.12 mg/g. In addition, thermodynamics studies elucidated that the adsorption process was spontaneous, randomness and endothermic process. Interestingly, the developed adsorbent retained respectable adsorption properties with acceptable removal efficiency exceeded 58% after ten sequential cycles of reuse. Besides, the results hypothesize that the adsorption process occurs via electrostatic interactions, reduction of Cr(VI) to Cr(III) and ion-exchanging. These findings substantiate that the ATP@Fe3O4-NH2Cs composite could be effectively applied as a reusable adsorbent for removing of Cr(VI) ions from aqueous solutions.