The decolorization of the remelted syrup is the most critical step in the sugar making process and directly affects the quality of refined sugar. Adsorption is a useful method that can be used to decolor the syrup. Guangxi University and queensland University of Technology, Brisbane, Australia, have jointly prepared quaternary ammonium functionalized chitosan (CS)/graphene oxide (GO) composite aerogel (GO-QACSA) as an effective green adsorbent for removing high molecular weight reducing glycobase degradation products (HRSADPs), the main colorants in remelted syrups.
Aerogels are attracting attention for their unique properties such as low density, high specific surface area, and large porosity. Aerogels have been widely used in many fields such as drug delivery, tissue engineering, catalyst carriers, and electrochemistry. It is also used in the manufacture of adsorbents. CS-based aerogels can be effectively used in the field of sugar refining to decolor remelt syrup. The introduced target function (quaternary ammonium) group can be easily ionized to form a positively charged quaternary ammonium ion that can effectively adsorb negatively charged colorants at pH suitable for (neutral) processing of sugar juice. GO is an oxygen-rich carbonaceous layered material. Since it can be used as an effective adsorbent, it has received considerable attention. Its high adsorption capacity can be attributed to the presence of a large number of oxygen atoms protruding from the layer. Oxygen atoms are present in epoxy, hydroxyl and carboxyl groups on the substrate and at the edges of the sheet. GO embedded in CS-based aerogels to form a homogeneous system helps enrich the pore structure of the aerogel and increases the strength of the polymer composites. Therefore, it can effectively improve the efficiency of aerogel as a decolorizer.
The advantages of GO-QACSA's removal of HRSADPs can be attributed to their well-connected 3-D network-like porous structure, non-toxic, high hydrophilicity and rich quaternary ammonium groups. The equilibrium adsorption capacity of GO-QACSA on HRSADPs reached 364.09 mg/g, and the removal rate >90%. GO-QACSA exhibits ultra-fast adsorption rates. Recovery experiments have shown that GO-QACSA exhibits good reproducibility and reusability. The authors studied the interaction mechanism of HRSADP adsorption on GO-QACSA, and the results showed that the two layers of HRSADPs adhered to the GO-QACSA surface by the electrovalent bonds formed between quaternary ammonium groups and carboxylic acid foundation groups. The average of 2-3 carboxylate ions in an HRSADP molecule binds to the quaternary ammonium cation of GO-QACSA. Based on the optimally fitted equilibrium isotherm, the authors propose four phenomenological mathematical models, namely external mass transfer resistance (EMTR), internal mass transfer resistance (IMTR), EMTR-IMTR combination, and active site adsorption (AAS). These models can be used to provide new insights into the adsorption mass transfer behavior of the system.
Figure 2, (a) CSA, QACSA, and GO-QACSA on leaves. (b) SEM photomicrographs of CSA, QACSA, GO-QACSA, and GO-QACSA/HRSADP. (c) EDX element mapping images of C, N, O, and Cl in CSA, QACSA, GO-QACSA, and GO-QACSA/HRSADP.
Figure 4. (a) XRD spectra of GO, CS, QACSA, and GO-QACSA. (b) Weightlessness curves for CSA, QACSA and GO-QACSA. (c) FTIR spectra of CS, GO, GO-QACSA, and GO-QACSA/HRSADP. (d) C1s, (e) O1s and (f) N1s spectra of QACS. (g) C1s, (h) O1s and (i) N1s spectra of GO-QACSA. (j) C1s, (k) O1s and (l) N1s spectra of GO-QACSA/HRSADPs. (m) C1s and (n) O1s spectra of HRSADPs. (o) Cell viability after incubation with different concentrations of CS, GO-QACSA and styrene-based resin extracts.
Figure 8. (a) Chromatogram of HRSADP solution at 420 nm before and after GO-QACSA adsorption. HRSADP solution (b) in FEEM spectra before and after adsorption by GO-QACSA. (d) Photo of HRSADP solution before and after GO-QACSA adsorption for 5 and 30 min. (e) Effect of the GO-QACSA regeneration cycle on the efficiency of HRSADP removal during adsorption equilibrium. (f) Effect of ionic strength on HRSADP removal efficiency of GO-QACSA at adsorption equilibrium. (g) Effect of sucrose concentration on HRSADP removal efficiency of GO-QACSA at adsorption equilibrium. Effect of GO-QACSA dose on (h) melanoid and (i) caramel removal under adsorption equilibrium. (j) Langmuir, Freundlich, and MLA modeled the description of HRSADP adsorption to GO-QACSA.
The paper was published in Chemical Engineering under the title High-performance quaternary ammonium-functionalized chitosan/graphene oxide composite aerogel for remelt syrup decolorization in sugar refining Journal. The correspondent is Dr. Li Wen of Guangxi University for Nationalities.
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doi.org/10.1016/j.cej.2021.132575