Construction of pH-responsive chlorpyrifos hydrogels system and its controlled-release property
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摘要: 传统农药易受到环境因子的影响而过早降解，导致利用率低下，利用响应型控释技术对传统农药剂型进行改善是提高农药利用率的有效措施。本研究使用多巴胺改性凹凸棒负载毒死蜱 (CPF)，将海藻酸盐作为包覆材料，利用外源挤出法与Ca2+ 交联，制备了能够对碱性条件作出特定响应的多巴胺改性凹凸棒/毒死蜱/海藻酸钙复合水凝胶 (PRCH)。通过扫描电镜 (SEM)、ζ-电位和比表面积测试 (BET) 对PRCH的形貌和结构进行表征，并研究PRCH在不同pH环境介质中的缓释性能、溶胀性能以及在紫外光和不同温度下的稳定性。结果表明：PRCH对毒死蜱的负载率高达85%，并能够在碱性条件下吸水溶胀，导致海藻酸钙孔道打开甚至结构坍塌，从而释放出毒死蜱。利用Korsmeyer-Peppas模型方程拟合曲线阐释PRCH的缓释机理为：在pH = 5.5的缓冲液中，毒死蜱的释药速率由药物的扩散和水凝胶溶胀共同决定；pH = 7.0时农药传输过程由水凝胶裂解的速率主导；而pH = 8.5时农药自身的扩散在毒死蜱的释放过程中起主要作用，但水凝胶的裂解加速了毒死蜱的扩散。PRCH比毒死蜱标准品拥有更强的紫外稳定性和温度稳定性。本研究表明，PRCH具备优异的载药性能、pH特定响应和绿色环保等优势，在提高传统农药施用稳定性和防治效果等方面具有良好的应用前景。Abstract: Traditional pesticides are susceptible to environmental factors and their early degradation leads to a low utilization rate. It is an effective measure to improve the utilization rate of pesticides by using responsive controlled release technology. In this study, dopamine-modified attapulgite/chlorpyrifos/calcium alginate composite hydrogels (PRCH) with a specific response to alkaline conditions were prepared using dopamine-modified attapulgite loaded with chlorpyrifos (CPF) and alginate was used as coating material by extrinsic extrusion method and crosslinking with Ca2+. The morphology and structure of PRCH were characterized by scanning electron microscope (SEM), Zeta-potential, and BET specific surface area tests. The sustained-release and swelling properties of PRCH in different pH environments were studied, and the stability of PRCH under UV light and different temperatures were explored. The results showed that the loading rate of PRCH with chlorpyrifos was as high as 85%. PRCH could absorb water and swell under alkaline conditions, resulting in the opening of calcium alginate channels and even structural collapse to release chlorpyrifos. The release mechanism of PRCH was explained by fitting the curve with Korsmeyer-Peppas model equation: The release rate of PRCH in buffer solution with pH 5.5 was determined by both drug diffusion and hydrogel swelling. When the buffer pH is 7.0, the pesticide transport process is dominated by the cleavage rate of hydrogels. At pH 8.5, the diffusion of pesticide itself played a major role in the release of chlorpyrifos, but the fragmentation of the hydrogels accelerated the spread of chlorpyrifos. In addition, we found that PRCH has stronger UV stability and temperature stability than industrial grade chlorpyrifos. Collectively, PRCH has the advantages such as excellent drug loading rate, pH-specific response characteristics and being environmentally friendly. Therefore, the system has great application prospects in improving the stability and efficacy of traditional pesticides.
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Key words:
- pH-responsive controlled release system /
- attapulgite /
- chlorpyrifos /
- alginate /
- hydrogels /
- slow release property
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图 1 海藻酸钙水凝胶在不同pH值的缓冲溶液中分子链变化示意图
Figure 1. Schematic diagram of molecular chain changes of calcium alginate hydrogels in buffer solutions with different pH values
图 2 海藻酸钙复合水凝胶制备流程图
Figure 2. Schematic diagram of the preparation process of calcium alginate composite hydrogels
图 3 经酸化 (HCl-ATP) 和未经酸化的凹凸棒 (ATP) 对20 g/L毒死蜱的负载能力
Figure 3. Load capacity of acidified (HCl-ATP) and unacidified attapulgite (ATP) with 20 g/L chlorpyrifos
图 4 经多巴胺修饰后的酸化凹凸棒对20、5和1 g/L毒死蜱的负载率
Figure 4. Load capacity of acidified attapulgite loaded with 20, 5 and 1 g/L CPF
图 5 (a) 凹凸棒 (ATP) 、 (b) 酸化凹凸棒 (HCl-ATP) 、 (c) 多巴胺修饰的凹凸棒 (PA) 、 (d) 负载毒死蜱的多巴胺修饰凹凸棒 (PA-CPF)、(e-f) PRCH和(g-i) PRCH截面的扫描电镜图
Figure 5. SEM of (a) attapulgite (ATP), (b) acidified attapulgite (HCl-ATP), (c) dopamine-modified attapulgite (PA), (d) dopamine-modified attapulgite located on chlorpyrifos (PA-CPF), (e-f) PRCH, (g-i) PRCH cross sections
图 6 ATP、HCl-ATP、PA、PA-CPF、CPF、PRCH的氮吸附-脱附曲线 (a) 及比表面积 (b) 和总孔容积和平均孔径 (c)
Figure 6. Nitrogen adsorption and desorption curves(a), specific surface area (b), total pore volume and average pore radius (c) of ATP, HCl-ATP, PA, PA-CPF, CPF and PRCH
图 7 ATP、HCl-ATP、PA、PA-CPF、PRCH和CPF的ζ电位
Figure 7. Zeta potentials of ATP, ATP-HCl, PA, PA-CPF, PRCH and CPF
图 8 ATP、PA、PA-CPF、CPF和PRCH的红外光谱图
Figure 8. IR spectra of ATP, PA, PA-CPF, CPF and PRCH
图 9 PRCH在pH = 5.5、7.0、8.5条件下CPF累积释放率(a)以及溶胀率(b)，PRCH在3种pH缓冲溶液中的状态图(c)
Figure 9. CPF cumulative release rates (a) and swelling rates (b) of PRCH in buffer solutions with pH = 5.5, 7.0, and 8.5, and digital photos of PRCH in buffer solutions with different pH values (c)
图 10 PRCH和毒死蜱在紫外光照射下的残留率(a)及其在45 ℃ (b)、25 ℃ (c)、5 ℃ (d)下的残留率
Figure 10. The residue rates of PRCH and CPF under UV irradiation (a) and the remaining rates at 45 ℃ (b), 25 ℃ (c) and 5 ℃ (d)
表 1 不同黏土矿物装载毒死蜱的能力
Table 1. Chlorpyrifos loading capacity of different clay minerals
矿物
Mineral负载率
Loading rate/%凹凸棒 Attapulgite 67.6 海泡石 Sepiolite 22.9 伊利石 Illite 19.8 蒙脱石 Montmorillonite 16.6 
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表 2 PRCH在pH值为5.5、7.0和8.5的3种介质中毒死蜱的累积释放曲线拟合参数
Table 2. Fitting parameters of cumulative release curves of chlorpyrifos by PRCH at pH 5.5, 7.0 and 8.5
pH 释药模型特征常数
K/h-n特性指数
n决定系数
R2扩散机制
Diffusion mechanism5.5 0.6156 0.6286 0.7179 Non-Fickian 7.0 0.3760 1.168 0.1281 Ⅱ-Fickian 8.5 21.35 0.3386 0.9293 Ⅰ-Fickian
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