Fabrication of a pH-Responsively Controlled-Release Pesticide Using

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Fabrication a pH-responsively controlled-release pesticide using an attapulgite-based hydrogel Yubin Xiang, Guilong Zhang, Chaowen Chen, Bin Liu, Dongqing Cai, and Zhengyan Wu ACS Sustainable Chem. Eng., Just Accepted Manuscript • DOI: 10.1021/ acssuschemeng.7b03469 • Publication Date (Web): 10 Nov 2017 Downloaded from http://pubs.acs.org on November 12, 2017

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ACS Sustainable Chemistry & Engineering

Fabrication a pH-responsively controlled-release pesticide using an attapulgite-based hydrogel

Yubin Xiang||,†,‡, Guilong Zhang||,†,§,#, Chaowen Chen†,‡, Bin Liu†,‡, Dongqing Cai*,†,§,#, Zhengyan Wu*,†,§,#

†Key

Laboratory of High Magnetic Field and Ion Beam Physical Biology, Hefei

Institutes of Physical Science, Chinese Academy of Sciences, Hefei 230031, People’s Republic of China ‡ University

of Science and Technology of China, Hefei 230026, People’s Republic of

China §Key

Laboratory of Environmental Toxicology and Pollution Control Technology of

Anhui Province, Hefei Institutes of Physical Science, Chinese Academy of Sciences, Hefei 230031, People’s Republic of China #Engineering

Laboratory of Environmentally Friendly and High Performance

Fertilizer and Pesticide of Anhui Province, Hefei Institutes of Physical Science, Chinese Academy of Sciences, Hefei 230031, People’s Republic of China

||Co-first

authors

*Corresponding authors. Email addresses: [email protected] (D.C.), [email protected] (Z.W.).

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ACS Paragon Plus Environment


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ABSTRACT: In this work, a pH-responsively controlled-release chlorpyrifos (PRCRC) was developed using a nanosystem consisting of chlorpyrifos (CPF), polydopamine (PDA), attapulgite (ATP), and calcium alginate (CA). Therein, CPF was adsorbed in the nanonetwork-structured PDA-modified ATP (PA) to obtain CPF-PA through hydrogen bonds and electrostatic attraction. Subsequently, CPF-PA combined with CA to form porous CPF-PA-CA hydrogel spheres (actually PRCRC) through crosslinking reaction, wherein PA acted as the skeleton. PRCRC spheres tended to collapse in alkaline solution and promoted the release of CPF, thus displayed a good pH-responsively controlled release performance, which was proved by the control efficacy test on grubs. Besides, the system could effectively protect CPF molecules from degradation under ultraviolet light. Importantly, the PA-CA hydrogel possessed a benign biocompatibility on E. coli and foxtail millet, showing a high biosafety. Therefore, this work provides a promising approach to improve the utilization efficiency and prolong duration of pesticide, which might have a huge potential application prospect. KEYWORDS: pH-responsively, controlled-release, CPF, utilization efficiency, biosafety.

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INTRODUCTION Pesticides are considered as the most effective way to control weeds, pests, and diseases in modern agriculture for the promotion of grain yield. However, traditional pesticides tended to enter environment easily through runoff, volatilization, and leaching, leading to serious environmental issues and even hazards to human beings.1 Consequently, it was urgent to develop new approaches to control the loss and improve the utilization efficiency of pesticide. Therein, a promising method to resolve this problem is construction of controlled-release pesticide systems, which will fulfill the demand of prolonging duration and enhancing utilization efficiency of pesticide. Recently, controlled-release nanopesticide, as one of the main trends of pesticide development, is attracting more and more attention all over the world.2,3 Therein, various kinds of nanomaterials have been used as carriers in those controlled-release pesticide systems such as polymer,4,5 inorganic nanmaterials,6 and nanocomposites.7 Although those technologies could reduce loss and improve the utilization efficiency of pesticide to a certain extent,8 there were still several dominant disadvantages hindering their large-scale applications: 1) difficulty to control the release and fulfill the demand,9 2) complicated process and high manufacture cost,10 3) potential risks of carriers to environment.11,12 Therefore, it is rather important to develop a nanopesticide system based on green nanocarrier with low cost, simple procedure, and controlled-release performance. Attapulgite (ATP), a hydrated magnesium aluminum silicate, possessed a unique fibrous morphology.13,14 Additionally, ATP displayed advantages of low cost, large storage, environmentally friendly property, and thus was widely used in water treatment, painting, sensor, and carrier.15-19 In the past few decades, ATP or organically-modified ATP were used as carriers for slow release pesticides mainly 3



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through adsorption.20 In our previous work, ATP with nano networks structure was used as a carrier to increase the adhesion ability of pesticide on crop leaf surface and thus reduce the migration and loss.21,22 However, these prepared ATP-pesticide systems could not respond to external stimulus (pH, temperature, light and so on) and thus lacked controlled-release property. Recently, a temperature-controlled-release herbicide was fabricated using ATP-based nanocomposite and could significantly increase utilization efficiency of herbicide.23 However, it seems to be difficult to conveniently regulate the temperature in practical application. Therefore, it is necessary to develop a facile method to control the release and improve the utilization efficacy of pesticide using ATP-based nanocomposites. Chlorpyrifos (CPF), a broad-spectrum organophosphate insecticide widely used in agriculture,24-26 displayed high toxicity to non-target organisms and human beings due to the effects such as teratogenicity, neurotoxicity, genotoxicity and so on.27-29 In addition, CPF tended to decompose under sunlight, resulting in decreasing of utilization efficiency.30 Therefore, it is of great significance to control the release of CPF and prevent CPF degradation under ultraviolet light, so as to enhance the utilization efficiency. This work attempted to develop a pH-responsively controlled-release CPF (PRCRC) via the incorporation of polydopamine (PDA)-modified ATP (PA), calcium alginate (CA), and CPF. PRCRC displayed a significantly higher utilization efficiency and control efficacy on pests compared with CPF. The morphologies and interactions of PRCRC system were investigated to reveal the mechanism. The fabrication process and mechanism of PRCRC were shown in Figure 1. Besides, the photostability under ultraviolet light and biocompatibility on E. coli and foxtail millet of the carrier were studied. This work provides a promising approach with low cost and simple procedure 4


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to improve the utilization efficiency of pesticide, which has a potential prospect in practical application. EXPERIMENTAL SECTION Materials. Natural ATP powder was provided by Mingmei Co., Ltd. (Anhui, China). CPF with purity of 99% was provided by Jinghong Chemical Co. Ltd (Jiangsu, China). Sodium alginate (MW=398.31), dopamine hydrochloride, CaCl2 and other chemicals were of analytical grade and purchased from Sinopharm Chemical Reagent Company (Shanghai, China). E. coli was provided by TransGen Biotech Co., Ltd (Beijing, China). Grubs were provided by Jiyuan Baiyun Industry Co., Ltd (Henan, China). Foxtail millet seeds were provided by Jiangsu Subei Flower Co., Ltd (Jiangsu, China). Deionized water was used throughout this work. Synthesis of PA. ATP powder (1.0 g) was dispersed ultrasonically in 50 mL of Tris-HCl buffer solution (pH 8.5, 10 mmol/L) and then dopamine hydrochloride (100 mg) was added. The resulting solution was stirred for 12 h in the dark at room temperature. Finally, PA was obtained after centrifugation at speed of 5000 r/min, washing with deionized water for three times, and drying in vacuum at 60oC overnight. Preparation of PRCRC Spheres. Firstly, PA (1.0 g) was immersed in CPF/ethanol solution (10 mL) with a concentration of 50 mg/mL in a sealed centrifuge tube and the suspension was shaken (150 rpm) overnight at room temperature, then CPF-PA was obtained after several washing-centrifugation cycles and drying at 60 oC. Afterwards, 0.5 g of as-prepared CPF-PA was dispersed in 50 mL of deionized water and then 0.5 g sodium alginate was added. The mixture was shaken (150 rpm) for 30 min to form a homogeneous suspension and injected into 100 mL of CaCl2 solution (0.1 mol/L) dropwise (10 μL each) using a syringe (20 mL, 5



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needle diameter of 1.2 mm) under continuous magnetic stirring (100 rpm) for 30 min. Finally, the formed spheres were filtered out, washed with deionized water for three times and subsequently freeze-dried to obtain PRCRC spheres with diameter of about 1-2 mm. The loading content (LC) and loading efficiency (LE) of CPF in PRCRC were calculated by equations31 (1) and (2) respectively: LC (%)=WCPF in PRCRC/WPRCRC100%

(1)

LE (%)=WCPF in PRCRC/Wtotal CPF100%

(2)

Where WPRCRC, WCPF in PRCRC, and Wtotal CPF were the weights of PRCRC, CPF in PRCRC, and total CPF respectively. Preparation of PA-CA. PA (0.5 g) was dispersed in 50 mL of sodium alginate aqueous solution (1.0 g/L) and the mixture was shaken (150 rpm) for 30 min to form a homogeneous suspension. Then the resulting suspension was injected into 100 mL of CaCl2 solution (0.1 mol/L) dropwise (10 μL each) using a syringe (20 mL, needle diameter of 1.2 mm) under continuous magnetic stirring (100 rpm) for 30 min. Afterwards, the formed spheres were filtered out, washed with deionized water for three times and subsequently freeze-dried. Finally, the resulting spheres were ground and passed through a sieve (200 mesh) to obtain PA-CA. Release Behavior Investigation. 50 mg of PRCRC was placed in 50 mL of tween (1.0 g/L) aqueous solution with pH of 5.5, 7.0, and 8.5 adjusted by phosphate buffer, respectively. Then the system was kept steadily at room temperature and 3 mL of the supernatant was taken out at given intervals, and then 3 mL of solution with the same pH was added to the corresponding system. Afterwards, CPF concentration was detected, and the cumulative release ratio (CRR) of CPF was calculated by equation (3):

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t 1   Ct  Vtotal   Ct  Vt 0 CRR(%)    m0  

    100%   

(3)

Where Ct (mg/mL) and Vt (3 mL) are the concentration and volume of the solution taken out at time t respectively, Vtotal (50 mL) is the volume of the total solution and m0 (mg) is the practical loading amount of CPF. Release kinetics investigation. The release kinetics of CPF from PRCRC was analyzed using Higuchi and Korsmeyer-Peppas models32 as followed: Higuchi model: Mt/M∞=kt1/2

(4)

Korsmeyer-Peppas model: Mt/M∞=ktn

(5)

Where Mt/M∞ is the fraction of released CPF until time t, k is kinetic constant, and n is an index which reflects release mechanism: Fickian diffusion (n

Fabrication of a pH-Responsively Controlled-Release Pesticide Using

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