Preparation And Catalytic Activity Of Functionalized Copper Alginate Double Network Catalysts

Sodium Alginate（SA）is a kind of natural polysaccharide refined from brown algae by alkali solution（usually Na OH）.Its molecular structure is composed of mannouronic acid（M unit）and its differential isomer Guluronic acid（G unit）,which has the characteristics of regeneration,biocompatibility and environmental friendliness.It is one of the biomass polysaccharides with the most development potential.A large number of carboxyl and hydroxyl groups are distributed on the main chain of sodium alginate,which can crosslink with bivalent or trivalent metal cations(Ca²⁺,Cu²⁺,Ni²⁺and Al³⁺,etc.)to form hydrogels with reticular structure.Therefore,sodium alginate can be used as a preferred metal catalyst carrier.The preliminary work of the research group shows that the copper alginate catalyst prepared with sodium alginate as precursor has good catalytic effect in the hydroxylation reaction of phenol.However,only four G segments on the two main chains in the sodium alginate structure can cross-link a metal ion,resulting in a low metal load of copper alginate catalyst（about 16%）.In addition,compared with alginate dry beads and powders,alginate aerogel has the advantages of large pore structure,high specific surface area,high thermal stability,low density and suitable chemical surface,and is more suitable for catalytic reactions.However,the mechanical properties of alginate aerogels are far from meeting the requirements of industrial applications.Therefore,the development of alginate aerogels with high activity and high strength has become a research focus.In this work,a alginate double network aerogel catalyst with high metal loading and high particle strength was developed.GO was prepared by one-pot method to enhance iminodiacetic acid functionalized copper alginate aerogel catalyst.Iminodiacetic acid changed the monocarboxyl group in the main chain of sodium alginate to the double carboxyl group through amidation reaction,and increased the number of functional groups of the metal that can be crosslinked in the aerogel,thus increasing the metal crosslinking content.The carboxyl functional groups on the surface of GO have the ability to decompose hydrogen peroxide and can act as a second catalytic active center in addition to metal ions to improve the mechanical strength of the aerogel catalyst.The physicochemical properties of the prepared aerogels were systematically characterized by FT-IR,XPS,NMR,mercury injection analysis,particle compression test and SEM,etc.Finally,the catalytic effect of the prepared aerogels was evaluated in the hydroxylation reaction of phenol with H₂O₂ as oxidant.The results showed that compared with the prepared functionalized copper alginate aerogel catalyst,the amount of copper ion cross-linking in the prepared functionalized copper alginate aerogel catalyst increased by 2 times（32.2%）and mechanical strength increased by 10 times.In the hydroxylation reaction of phenol,the conversion rate of phenol is up to 93.9%,and the selectivity of catechol（catechol and hydroquinone）can reach 98.2%.In addition,the catalytic activity of the aerogel catalyst only lost 5.8%after being recycled for 5 times in phenol hydroxylation reaction.In order to further improve the mechanical properties of the aerogel catalyst,polyacrylamide was introduced into the functionalized alginate aerogel.It was found that the introduction of polyacrylamide could effectively improve the mechanical strength of the aerogel,but it would affect the metal load.The double-network functionalized copper alginate aerogel catalyst provides an ideal material for the development of the next generation of biomass aerogel catalysts.