Comparing the efficiency of unmodified dried sludge adsorbents and those modified via chemical and microwave methods in removing 2,4-dinitrophenol from aqueous solutions

Enhanced phytoremediation of 2,4-DNP-contaminated wastewater by Salix matsudana Koidz with MeJA pretreatment and associated mechanism

2,4-Dinitrophenol (2,4-DNP) is recognized as an emerging contaminant due to its high toxicity and poor biodegradability, posing a threat to animals, plants, and human health. The efficient removal of 2,4-DNP remains a challenging issue in phytoremediation research, particularly because of its toxic effects on plants. To address this, a hydroponic simulation experiment was conducted to investigate the impact of adding exogenous methyl jasmonate (MeJA) on the tolerance and purification capabilities of Salix matsudana Koidz (S. matsudana) seedlings exposed to 2,4-DNP. The results indicated that the addition of exogenous MeJA mitigated the damage caused by 2,4-DNP to S. matsudana seedlings by enhancing the activity of antioxidant enzymes, reducing excess reactive oxygen species (ROS), lowering membrane lipid peroxidation, and minimizing membrane damage. Notably, the most effective alleviation was observed with the addition of 50 mg·L-1 MeJA. Furthermore, exogenous MeJA helped maintain the biomass indices of S. matsudana seedlings under 2,4-DNP stress and increased the removal efficiency of 2,4-DNP by these seedlings. Specifically, the addition of 50 mg·L-1 MeJA resulted in a removal percentage of 79.57%, which was 11.88% higher than that achieved with 2,4-DNP treatment. In conclusion, exogenous MeJA can improve the plant resistance and enhance 2,4-DNP phytoremediation.

Cu2+, Cr3+, and Ni2+ in mono- and multi-component aqueous solution adsorbed in passion fruit peels in natura and physicochemically modified: a comparative approach

Among the low-cost adsorbent are agricultural residues, which can be used in natura or modified forms. This work evaluated the adsorption of Ni2+, Cu2+, and Cr3+ in mono- and multi-component aqueous solutions using passion fruit peels in natura (Nat-PF) and physicochemically modified (Mod-PF). The adsorption was investigated by kinetic and isotherm models. A comparative investigation was conducted to analyze the effect of the experimental conditions by statistical test, adsorption capacity ratio, selectivity of adsorbate, and distribution coefficient. In both adsorbents, the process occurs in monolayer by chemosorption. Equilibrium was reached after 30 min, with highest adsorption capacity for Cu2+ as 0.495 mg g-1, for Cr3+ as 0.483 mg g-1, and for Ni2+ as 0.464 mg g-1. The adsorption in Mod-PF was less affected in multi-component solutions, reducing the adsorption capacity by 0.06-0.15 times when compared to monocomponent solutions, while in Nat-PF a reduction of more than half of adsorption capacity was obtained. The modifications imposed on the biomass led to a change in its adsorptive selective, being Cr3+  > Cu2+  > Ni2+ for Nat-PF and Cu2+  > Ni2+  > Cr3+ for Mod-PF.

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.

The superior adsorption capacity of 2,4-Dinitrophenol under ultrasound-assisted magnetic adsorption system: Modeling and process optimization by central composite design

2,4-Dinitrophenol (DNP) was listed as a priority pollutant; accordingly, DNP-contaminated effluent must be treated before discharging to the receiving resources. In the present study, the hybrid ultrasound-assisted GO-Fe₃O₄ system was employed to decontaminate DNP solution. Ultrasound irradiation makes the mass transfer of adsorbate improved and Fe₃O₄ enables GO separation from liquid phase under external magnetic field. The as-synthesized GO-Fe₃O₄ composite was characterized by SEM, TEM, XRD, FTIR, BET and VSM. A response surface methodology based central composite design (RSM-CCD) was used to estimate and optimize of various variables on DNP removal percentage. Under optimal conditions (pH: 4.45, adsorbent dose: 0.178 g/L, ultrasound frequency: 40.02 kHz and DNP concentration: 50.10 mg/L, maximum adsorption capacity was calculated to be 425.58 mg/g for the ultrasound system, higher than the simple system 309.40 mg/g, indicating the importance of synergistic effect between the ultrasound waves and the adsorption process. The ultrasound-assisted adsorption system showed the better agreement with the Langmuir isotherm (R² > 0.997), while the results of the stirring system were more consistent with the Freundlich model (R² > 0.991). The experimental results indicated that the pseudo-second-order kinetic model well fitted by experiment data and rate constant was calculated to be 0.000148 min^-1 and 0.000002 min^-1 under ultrasound and silent systems, respectively. The rate of desorption under ultrasound was more favorable and reuse of the adsorbent in both systems after 10th consecutive cycles reduced by about 22%. Thermodynamic calculations also confirmed the endothermicity and spontaneity of both systems. Electrostatic attraction, hydrogen bonding, and π -π interactions played key roles during the adsorption of DNP onto the MGO. In conclusion, the outcomes of this study provide valuable information of the ultrasound-assisted GO-Fe₃O₄ system for practical applications.