for catalyzing the reactions. These compounds can be redox active in solution by electrochemical oxidation because of its multielectron property, while their anion structure is preserved (Chen et al. 2019; Glass et al. 2016). POMs have been used for the degradation of biomass (Albert et al. 2012; Bosco et al. 2010; Zhang et al. 2012). Thus, Liu et al. used phosphomolybdic acid (H 3 PMo 12 O 40 , abbreviated as PMo 12 ) to degrade biomass such as cellulose and starch into small molecules of sugars and organic acids (Liu et al. 2016). Tian et al. hydrolyzed cellulose with phosphotungstic acid (H 3 PW 12 O 40 ) at 180 °C for 120 min. The glucose yield was more than 50% with 92.3% glucose selectivity, and few byproducts were obtained (Tian et al. 2010). Starch and cellulose are high molecular polymers formed by dehydration of glucose units (Buléon et al. 1998; Goodman 2020). Therefore, POMs can be used to hydrolyze starch to produce reducing sugar (RS) (Mamman et al. 2008; Mua and Jackson 1997) and glycolic acid(Zhang et al. 2012), having demonstrated excellent electrochemical performance on the degradation of biomass. Herein, recycled waste starch (WS) in OCC pulping process water was oxidized and degraded using PMo 12 . The in § uencing factors, namely, reaction temperature, time, and PMo 12 usage, on the production of RS and glycolic acid from WS were evaluated. Furthermore, the recycling performance of PMo 12 after electrooxidation regeneration was analyzed. The feasibility of turning WS to RS and glycolic acid using PMo 12 was studied. The speci ¦ c experimental process is presented in Fig. 1. This work is expected to provide a theoretical guidance and application reference for realizing resource utilization of WS in the OCC pulping process water and developing clean papermaking production. Materials And Methods Materials WS from OCC pulping process water was provided by Nine Dragons Paper Co., Ltd (Taicang, China). PMo 12 was supplied by Shanghai Aladdin Chemicals Co., Ltd. (Shanghai, China). Glucose (AR), cesium chloride (CsCl, AR), and diethyl ether (AR) were purchased from Sinopharm Chemical Reagent Co., Ltd. (Shanghai, China). 3, 5-Dinitrosalicylic acid (DNS) was prepared according to a previous work (Adeogun et al. 2019; Miller 1959).
Curve determination of glucose standard solution
Glucose (1 g) was added to a volumetric § ask, and deionized (DI) water was added to obtain a volume of 1 L. From this solution, which was labeled as standard solution, 0, 0.2, 0.4, 0.6, 0.8, and 1.0 mL was taken respectively, supplemented with DI water to 1 mL, and 2 mL DNS was added. After reaction in boiling water bath for 2 min, the solution was placed in an ice water bath. Finally, the reaction solution was ¦ xed to 15 mL. The absorbance of the mixture was measured using a UV757CRT Model spectrophotometer at 540 nm (Miller 1959; Tian et al. 2010). The DNS reagent reacted with RS to form 3-amino-5-nitrosalicylic acid. The product was brownish red under boiling condition, and the color was proportional to the RS content in a certain concentration range.
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