Influence of Pyrolysis Parameters Using Microwave toward Structural Properties of ZnO/CNS Intermediate and Application of ZnCr2O4/CNS Final Product for Dark Degradation of Pesticide in Wet Paddy Soil

Pesticide is a pollution problem in agriculture. The usage of ZnCr2O4/CNS and H2O2 as additive in liquid fertilizer has potency for catalytic pesticide degradation. Colloid condition is needed for easy spraying. Rice husk and sawdust were used as carbon precursor and ZnCl2 as activator. The biomass–ZnCl2 mixtures were pyrolyzed using microwave (400–800 W, 50 min). The products were dispersed in water by blending then evaporated to obtain ZnO/CNS. The composites were reacted with KOH, CrCl3·6H2O, more ZnCl2, and little water by microwave (600 W, 5 min). The ZnCr2O4/CNS and H2O2 were used for degradation of buthylphenylmethyl carbamate (BPMC) in wet deactivated paddy soil. TOC was measured using TOC meter. The FTIR spectra of the ZnO/CNS composites indicated the completed carbonization except at 800 W without ZnCl2. The X-ray diffractograms of the composites confirmed ZnO/CNS structure. SEM images showed irregular particle shapes for using both biomass. ZnCr2O4/CNS structure was confirmed by XRD as the final product with crystallite size of 74.99 nm. The sawdust produced more stable colloids of CNS and ZnO/CNS composite than the rice husk. The pyrolysis without ZnCl2 formed more stable colloid than with ZnCl2. The ZnCr2O4/CNS from sawdust gave better dark catalytic degradation of BPMC than from rice husk, i.e., 2.5 and 1.6 times larger for 400 and 800 W pyrolysis, respectively.

Synthesis of MFe2O4/CNS (M = Zn, Ni, Mn) Composites Derived from Rice Husk by the Hydrothermal-Microwave Method for Remediation of Paddy Fields

In this research work, MFe2O4/CNS was prepared using the hydrothermal–microwave method. The influence of cations (M) toward functional groups of composites and their performance in pesticide degradation were studied. Rice husk was pyrolyzed hydrothermally (200 °C, 6 h) and by microwave (800 W, 40 min). Each product was mixed with MCl2 (Zn, Ni, Mn), FeCl3, KOH, and water, and calcined (600 °C, 15 min) to obtain a composite. Characterization by XRD confirmed the MFe2O4/CNS structure. The FTIR spectra of the composites showed different band sharpness related to C-O and M-O. A mixture of dried paddy farm soil, composite, BPMC (buthylphenylmethyl carbamate) pesticide solution (0.25%), and H2O2 solution (0.15%) was kept under dark conditions for 48 h. The solution above the soil was filtered and measured with a UV-Vis spectrophotometer at 217 nm. Applications without the composite and composite–H2O2 were also conducted. The results reveal that dark BPMC degradation with the composite was 7.5 times larger than that without the composite, and 2.9 times larger than that without the composite–H2O2. There were no significantly different FTIR spectra of the soil, soil–BPMC, soil–BPMC-H2O2, and soil–BPMC-H2O2 composite and no significantly different X-ray diffractograms between the soil after drying and soil after application for pesticide degradation using the composite.

Oxidative Treatments of Pesticides in Rainwater Runoff by HOCl, O3, and O3/H2O2: Effects of pH, Humic Acids and Inorganic Matters

This study systematically investigated the oxidative treatment of five selected pesticides, alachlor (ALA), carbendazim (CAR), diuron (DIU), pyrimethanil (PYR), and tebuconazole (TEB), by comparing their relative reactivities as a function of three different oxidative treatment processes (i.e., chlorine (HOCl), ozone (O3), and ozone/hydrogen peroxide (O3/H2O2)) under various oxidant dosages, reaction times, and pH conditions. For oxidative treatment, pesticide standards were spiked into rainwater. The removal efficiency of the selected pesticides varied considerably depending on the oxidative treatment processes. HOCl, O3, and O3/H2O2 treatments were highly effective at eliminating CAR (>80%) and PYR (>99%), while they were not significantly effective in removing TEB (<20%). In the case of DIU, HOCl (81%) was shown to be more effective than O3 (24%) and O3/H2O2 (49%). The removal efficiency of ALA was in the order of O3/H2O2 (49%) > O3 (20%) > HOCl (8.5%). The effect of increasing the solution pH from 5.0 to 9.0 on pesticide degradation varied between the oxidative treatment processes. Additionally, NH4+, NO2−, and humic acid in rainwater significantly inhibited pesticide degradation.

Effects of Different Types of Zeolites on the Degradation Kinetics of Malathion Pesticide in Water

The study examined the effects of selected types of zeolites as an environmentally benign and friendly way to degrade, S-1, 2-bis (ethoxycarbonyl) ethyl O, O-dimethylphosphorodithioate (malathion), used as a model pesticide, from river water. The effect of the size of zeolite channels and dimensionality (such as 1D, 2D, and 3D), Si/Al ratio, and operating pH were studied to find a suitable type of zeolite and conditions to optimize the pesticide degradation. Mordenite (MOR (1D): Si/Al=6.83, and Si/Al=10.72), ferrierite (FER (2D): Si/Al=10.71), ZSM-5 (MFI (3D): Si/Al=6.83 and Si/Al=10.72) and USY (FAU (3D): Si/Al=2.77) zeolites were individually mixed with a water sample collected from Monjolinho River in São Carlos (SP), Brazil and the degradation trend studied. The results showed that all the zeolites accelerated the degradation of malathion. Nevertheless, lower zeolite Si/Al ratio and larger 3D channels or cavities had a positive influence on the degradation rate. The FAU zeolite presented the stronger degradation of the malathion with a half-life of 16.5 followed by ZSM-5 with 24.8, ferrierite with 29.7, and finally mordenite with 30.3 hours.