Sci­en­tists Eye Cheaper Ad­sor­bents

Chemical Industry Digest - - New Developments -

Ateam of re­searchers from the Chem­istry for Tech­nolo­gies Lab­o­ra­tory and the De­part­ment of Me­chan­i­cal and In­dus­trial En­gi­neer­ing, Univer­sity of Bres­cia, Italy, has de­vel­oped a new class of low-cost and sus­tain­able ab­sorbents that could re­place ac­ti­vated car­bon in many waste­water and air pol­lu­tion treat­ment ap­pli­ca­tions.

One of the most com­monly used ad­sor­bents is ac­ti­vated car­bon, well-known for its high ad­sorp­tion ca­pac­ity for dyes, or­ganic con­tam­i­nants and heavy met­als. How­ever, it is ex­pen­sive to pro­duce and re­gen­er­ate, and can cre- ate dis­posal prob­lems.

The re­searchers con­sid­ered var­i­ous nat­u­ral re­sources and by-prod­ucts from in­dus­trial pro­cesses that could be used as cost-ef­fec­tive and more en­vi­ron­men­tally-friendly re­place­ments. The re­sult is an eas­ily syn­the­sized, por­ous, low-cost hy­brid ma­te­rial that can act as ad­sor­bent and fil­ter for or­ganic com­pounds re­moval, both from the air and waste­water. The hy­brid ma­te­rial is ob­tained by com­bin­ing sodium al­gi­nate - a nat­u­rally oc­cur­ring, highly abun­dant and in­ex­pen­sive polysac­cha­ride with the amor­phous sil­ica fume, a byprod-

uct de­rived from fer­rosil­i­con or sil­i­con metal al­loy pro­cess­ing.

Sodium al­gi­nate, read­ily ex­tracted from var­i­ous species of al­gae and sea­weeds, has long been the fo­cus of in­ten­sive re­search due to its gelling ca­pac­ity, film form­ing, emul­sion sta­bi­liz­ing, bio­com­pat­i­bil­ity, and non-tox­i­c­ity prop­er­ties. How­ever, its me­chan­i­cal strength of­ten is an is­sue; re­search to over­come the prob­lem in­cludes cross link­ing, blend­ing with hy­drophilic ma­te­ri­als and nano-re­in­force­ment to pro­duce nano-com­pos­ites. Also in­cluded in this re­search is al­gi­nate’s abil­ity to form or­ganic/in­or­ganic com­pos­ites - par­tic­u­larly with sil­ica. These com­pos­ites of­fer many ad­van­tages in terms of chem­i­cal and me­chan­i­cal sta­bil­ity. How­ever, man­u­fac­ture of such com­pos­ites can in­volve sol­vents and pre­cip­i­tat­ing agents that im­pact both their en­vi­ron­men­tal and eco­nomic ben­e­fits.

What the Ital­ian re­searchers have achieved is a sim­ple, patent-pend­ing syn­the­sis of a new por­ous hy­brid ma­te­rial us­ing sodium al­gi­nate and sil­ica fume. The ma­te­rial is con­sol­i­dated by the gelling prop­er­ties of al­gi­nate and by de­com­po­si­tion of sodium-bi­car­bon­ate con­trolled poros­ity at low tem­per­a­tures (70–80°C). The struc­tural, ther­mal, and mor­pho­log­i­cal char­ac­ter­i­za­tion shows that the ma­te­rial is a meso­porous (hav­ing pore di­am­e­ters of 2–50nm) or­ganic/in­or­ganic hy­brid, as pub­lished in Fron­tiers in Chem­istry.

“This pa­per shows the sim­ple syn­the­sis of a new por­ous hy­brid ma­te­rial, ob­tained by us­ing low cost and by-prod­uct ma­te­ri­als,” said lead au­thor, Elza Bon­tempi from the Univer­sity of Bres­cia. “The ma­te­rial was de­signed on the ba­sis of the Euro­pean Com­mis­sion’s re­quest to de­velop an af­ford­able, sus­tain­able and in­no­va­tive de­sign-driven ma­te­rial so­lu­tion that can re­duce the con­cen­tra­tion of par­tic­u­late mat­ter in ur­ban ar­eas. The ar­ti­cle re­ports pre­lim­i­nary re­sults about the new ma­te­rial’s ca­pa­bil­ity to cap­ture par­tic­u­late mat­ter. It can also be used for waste­water re­me­di­a­tion. In par­tic­u­lar, its abil­ity to re­place ac­ti­vated car­bon is demon­strated,” she added.

The syn­the­sis method is sim­ple and easy to scale up. Tak­ing ad­van­tage of the gelling prop­er­ties of al­gi­nate, the re­searchers com­bined it with the de­com­po­si­tion of food-grade sodium bi­car­bon­ate (bak­ing soda) to con­sol­i­date the ma­te­rial. Test­ing of waste­water pol­lu­tion was per­formed us­ing methy­lene blue dye as a model pol­lu­tant. The hy­brid ma­te­rial ad­sorbed and re­moved the dye, even at high con­cen­tra­tions, with 94% ef­fi­ciency. Fur­ther, coat­ing the ma­te­rial with a 100-nm thin film of ti­ta­nia im­parts good photo degra­da­tion of pol­lu­tants (more than 20%).

Anal­y­ses have re­vealed that, com­pared with ac­ti­vated car­bon, pro­duc­tion of the hy­brid ma­te­rial con­sumed less en­ergy while leav­ing a much smaller car­bon foot­print. The ma­te­rial also demon­strated en­cour­ag­ing ca­pa­bil­i­ties for trap­ping diesel-ex­haust-fume par­tic­u­late mat­ter. The hy­brid ma­te­rial can be ap­plied as a coat­ing, used for spray­ing or brush­ing, or 3-Dprinted. This means it could be used to cover ex­ter­nal build­ing sur­faces to re­move par­tic­u­late mat­ter, as well as in the de­sign of novel wa­ter fil­tra­tion units. This ver­sa­til­ity, said Bon­tempi, makes it an ex­cit­ing new ad­di­tion to the tool­kit for re­duc­ing air and wa­ter pol­lu­tion.

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