**4. Conclusions**

The preparation of a composite with a covalent biopolymer framework (CBF) was achieved by the formation of amide linkages between pectin and chitosan using a sonication-assisted synthesis in DMSO. By contrast, the use of water as a solvent with conventional heating yielded pectin–chitosan polyelectrolyte complexes (PECs). Characterization of the covalent and ionic types of pectin–chitosan composites was supported by TGA results that revealed a more thermally stable cross-linked composite with a covalent framework (PC11 S DMSO) over the pectin–chitosan polyelectrolyte complex (PC11 W) prepared in water. The IR intensity changes for the secondary amine groups of chitosan before and after composite formation provided support for the two types of composites (CBFs and PECs). Amide-based CBFs prevail in DMSO, while PECs are favored in water-based reactions. The MB uptake capacity for the pectin–chitosan CBFs exceed that of the PECs due to the key role of the carboxylate anions of pectin. The greater dye uptake capacity of pectin highlights the prominent role of the carboxylate anion site accessibility in the CBF composites versus the PEC-based materials. The formation of an amide-based covalent network results in greater pectin incorporation onto chitosan with secondary adsorption sites along the chitosan backbone. The use of a solvent to bias the formation of CBFs versus PECs in the case of pectin–chitosan composites will contribute to the rational design of materials with improved properties for diverse adsorption-based applications. This includes solid phase extraction and recovery processes due to enhanced phase separation and the removal efficiency of waterborne species that possess positive electrostatic potential.

**Author Contributions:** Conceptualization, L.D.W.; methodology, L.D.W. and D.K.; software, D.K.; validation, L.D.W. and D.K.; formal analysis, D.K.; investigation, L.D.W. and D.K.; resources, L.D.W.; data curation, L.D.W.; writing—original draft preparation, D.K.; writing—review and editing, L.D.W. and D.K.; visualization, D.K.; supervision, L.D.W.; project administration, L.D.W.; funding acquisition, L.D.W. All authors have read and agreed to the published version of the manuscript.

**Funding:** Lee D. Wilson acknowledges the support granted by the Government of Canada through the Natural Sciences and Engineering Research Council of Canada (Discovery Grant Number: RGPIN 2016-06197).

**Acknowledgments:** The authors acknowledge the support provided by the Saskatchewan Research Council and the University of Saskatchewan.

**Conflicts of Interest:** The authors declare no conflict of interest.
