Preparation And Functional Activity Of Imine Functionalized Metal-crosslinked Alginates Catalyst

Alginate(ALG)is a natural unbranched polysaccharide derived from various algae and bacterial sources.Algae is abundant in water,so the reserves of alginate in the natural world are huge,the annual production of ALG is about 30,000 tons in industrial production.Alginate is widely used in many fields such as food,medicine,agriculture and industry because of its non-toxicity,gel-forming,film-forming,stickiness,safety,biocompatibility and biodegradability.Meanwhile,ALG can also be used for wastewater treatment,toxic metal adsorption,medicine carrier,etc.As a biomass polymer,in recent years,sodium alginate(Na-ALG)is a biopolymer with a wide range of applications.Therefore,more and more researchers pay attention to the application of Na-ALG in the field of catalyst carrier or catalyst.However,as a catalyst,the main challenge of Na-ALG is low metal load amount and low catalytic activity.In our study,aldehyde groups are introduced into the Na-ALG molecule to form an alginate-based Schiff Base metal complex.The preparation method: firstly,sodium periodate and Na-ALG are reacted in different proportions to obtain alginate dialdehyde(ADA)with different oxidation degrees;secondly,amination of ADA with organic amines to form alginate-based Schiff Base(ADA-N);finally,ADA-N reacts with copper chloride solution to prepare imine functionalized metal-crosslinked alginates catalyst(Cu-ADA-N).Characterization of the structure and morphology of the catalyst using Nuclear magnetic resonance spectrometer(NMR),Fourier transform infrared spectroscopy(FT-IR),Ultraviolet visible spectrophotometer(UV-vis),X-ray photoelectron spectroscopy(XPS),Gel permeation chromatography(GPC),inductively coupled plasma atomic emission spectroscopy(ICP-AES),scanning electron microscope(SEM)and atomic force microscope(AFM).In addition,its catalytic performance in phenol hydroxylation reaction is investigated.Results illustrate that ADA-N has more reactive groups compared with alginate.The metal loading of ADA-N is increased by 20%-30%,and the conversion of phenol in the catalytic reaction is increased by more than 20%.Different degrees of oxidation of ADA have a significant effect on metal loading of the catalyst.The catalyst with the highest oxidation degree of ADA prepared is 11.2% higher than the lowest.The phenol conversion rate of the latter is 33.7% higher than that of the former.In the catalyst reusability study,it is found that the conversion of phenol decreased by only 4.5% after repeated use of CuADA-N-106 five times.