基于光谱分析探讨磷酸与焦磷酸改性生物炭的磷素形态

通过磷酸（H₃PO₄）和焦磷酸（H₄P₂O₇）对生物炭改性能够使其更适于农业应用。探明H₃PO₄和H₄P₂O₇改性生物炭的P赋存形态与结合方式，将有助于揭示其表面P的生物有效性。以麦秆生物炭（WBC）与棉秆生物炭（CBC）为原料，分别通过H₃PO₄和H₄P₂O₇制备了H₃PO₄改性生物炭（P-WBC和P-CBC）和H₄P₂O₇改性生物炭（PA-WBC和PA-CBC）。利用拉曼光谱（Raman）与扫描电镜能谱（SEM-EDS）对改性生物炭结构与P分布变化进行表征，采用傅里叶红外光谱（FTIR）和X射线光电子能谱（XPS）探究改性生物炭表面P结合方式，并结合Hedley磷分级方法与可见分光光度法，定量分析改性前后生物炭中P形态及含量变化。结果表明，H₃PO₄和H₄P₂O₇改性后生物炭I_G/I_D值增大，石墨化结构增强，形成了含P颗粒状结构。H₃PO₄和H₄P₂O₇改性促进了生物炭表面羧基（—COOH）、P—O—P和P—H等酸性官能团与含P基团的形成，且H₃PO₄改性生物炭和H₄P₂O₇改性生物炭表面官能团种类相似。XPS结果显示，与WBC和CBC相比，改性处理中的O(1s)峰相对含量显著增加了13.15%~32.44%，P(2s)峰相对含量显著增加了18.54%~27.02%（p<0.05）。反褶积分峰将P(2s)与O(1s)分为C—P—O，C—O—P，OPO，CO与（或）PO，C—O—C与（或）P—O—C和P—O—P六类。较H₃PO₄改性而言，H₄P₂O₇改性能够促进更多C—O—P，OPO，C—O—C与（或）P—O—C和P—O—P键的形成。改性也使得生物炭中总P含量显著增加，且PA-WBC和PA-CBC中P含量显著高于P-WBC和P-CBC。与WBC和CBC相比，改性处理中活性P含量显著提高2.36~14.77 g·kg-1，稳定态P含量显著降低0.06~0.17 g·kg-1（p<0.05）。与P-WBC和P-CBC相比，PA-WBC和PA-CBC的活性P、中等活性P分别显著增加了5.27~15.66和0.53~0.64 g·kg-1, 稳定态P含量减少了0.03~0.34 g·kg-1（p<0.05）。H₃PO₄和H₄P₂O₇改性改变了P在生物炭表面的结合方式，同时增加了P的活性。H₃PO₄和H₄P₂O₇改性生物炭间，不同形态P含量和结合方式的差异对进一步探究P的生物有效性具有重要意义。

Phosphorus Species of Biochar Modified by Phosphoric Acid and Pyrophosphoric Acid Based on Spectral Analysis

They can be applied to agriculture by changing the properties of biochar by phosphoric acid (H₃PO₄) and pyrophosphoric acid (H₄P₂O₇) . It is helpful to revealing the bio-availability of P on its surface for identifying P occurrence form and binding mode of changed biochar for H₃PO₄ and H₄P₂O₇. This paper adopts wheat stalk biochar (WBC) and cotton stalk biochar (CBC) as raw materials. Meanwhile, this paper prepares changed H₃PO₄ (P-WBC and P-CBC) and changed biochar of H₄P₂O₇ (PA-WBC and PA-CBC) by H₃PO₄ and H₄P₂O₇ respectively. This paper adopts Raman spectroscopy (Raman) and scanning electron microscopy (SEM) to characterize the structure and P distribution of the changed biochar. In addition, this paper adopts Fourier transform infrared spectroscopy (FTIR) and X-ray photoelectron spectroscopy (XPS) to investigate the P-binding mode of changed biochar surface. Meanwhile, this paper quantitatively analyzes the changes of P form and content in biochar before and after changing by combining the Hedley phosphorus classification method with visible spectro-photometry. The result shows that the I_G/I_D value of biochar increases and the graphitization structure enhances to form the P-containing granular structure after changing the properties of H₃PO₄ and H₄P₂O₇. It has promoted the formation of carboxyl (—COOH), P—O—P and P—H acid functional groups on the surface of biochar for changes of H₃PO₄ and H₄P₂O₇. They are similar to functional groups on the surface of changed biochar of H₃PO₄ and changed biochar of H₄P₂O₇. XPS result shows that it increases by 13.15%～32.44% significantly by compared with WBC and CBC for the relative content of O1s peak in the changed treatment. Meanwhile, it also shows that it increases by 18.54%~27.02% significantly for the relative content of the P(2s) peak (p<0.05). They have divided P(2s) and O（1s） into C—P—O, C—O—P, OPO, CO and (or) PO, C—O—C and (or) P—O—C and P—O—P for the deconvolution integral peaks. It can promote the formation of C—O—P, OPO, C—O—C and/or P—O—C and P—O—P bonds for the changed properties of H₄P₂O₇ by comparing with the changed properties of H₃PO₄. It also significantly increases the total P content in biochar for the changed properties. Meanwhile, it is significantly higher than that in P—WBC and P—CBC for the P content in PA-WBC and PA-CBC. The active P content in the changed treatment significantly increases by 2.36~14.77 g·kg-1 compared with WBC and CBC. In addition, the stable P content significantly decreases by 0.06~0.17g·kg-1 (p<0.05). The active P and moderate active P of PA-WBC and PA-CBC significantly increase by 5.27~15.66 and 0.53~0.64 g·kg-1 respectively. The stable P content decreases by 0.03~0.34 g·kg-1 (p<0.05). In conclusion, it has changed the binding mode of P on biochar surface and increased the activity of P for the changed properties of H₃PO₄ and H₄P₂O₇. The difference in the content and binding mode of P in different forms between H₃PO₄ and H₄P₂O₇ modified biochar are of great significance for further exploring the bioarailability of P.