Modifikacija, karakterizacija i primena adsorbenata na bazi gljive Handkea utriformis za uklanjanje jona metala iz vode

Abstract

Predmet istraņivanja ove doktorske disertacije je modifikacija alkalno aktiviranog subglebalnog tkiva gljive Handkea utriformis aluminijum–oksidom i hidroksiapatitom (HAp) i ispitivanje adsorpcije jona Pb2+, Cd2+ i Ni2+ na dobijenim materijalima u poreĊenju sa adsorpcijom na polaznim materijalima. Navedeni materijali su izabrani zbog netoksiĉnosti, niske cene, hemijske i termiĉke stabilnosti, kao i mogućnosti dobijanja iz prirodnih izvora i otpada. Dosadańnja istraņivanja su potvrdila da γ–aluminijum–oksid (γ–Al2O3) i HAp, u razliĉitim oblicima, imaju afinitet za adsorpciju jona metala iz vodenih rastvora i da se kapacitet adsorpcije povećava sa smanjenjem veliĉine ĉestica. MeĊutim, velika sklonost ka aglomeraciji veoma finih ĉestica dovodi do stvaranja agregata, ńto smanjuje povrńinu dostupnu za adsorpciju, pa samim tim i njihove adsorpcione sposobnosti. Sa ciljem da se spreĉi stvaranje agregata i poveća adsorpcioni kapacitet, tkivo alkalno aktivirane subglebe gljive Handkea utriformis je korińćeno kao nosaĉ za HAp i materijale na bazi γ–Al2O3. Poroznost i broj povrńinskih funkcionalnih grupa (amino i hidroksilnih) subglebe (Su) je povećan alkalnom aktivacijom (Sa). Hemijska analiza subglebe je potvrdila prisustvo polisaharida i proteina, odnosno funkcionalnih grupa pogodnih za adsorpciju katjona metala iz vode, ali i za dalju modifikaciju u cilju dobijanja materijala sa boljim adsorpcionim svojstvima. Poboljńanje adsorpcionih svojstava aluminijum–oksida je ostvareno sintezom trodimenzionalnog makroporoznog (3DOM) γ–aluminijum–oksida strukturno modifikovanog gvoņĊe(III)–oksidom, (Al,Fe)2O3, a zatim i povrńinski aminosilanom, (Al,Fe)2O3APTES. Povrńinskom modifikacijom su uvedene amino funkcionalne grupe, ĉime je izvrńen dodatan uticaj na poboljńanje adsorpcionih svojstava prema ispitivanim katjonima, ali i ostvarena mogućnost kovalentnog vezivanja na alkalno aktiviranu povrńinu subglebe preko 3–(karbometoksi) propanoil hlorida (CPC), (SaCPC–(Al,Fe)2O3APTES). Sinteza 3DOM (Al,Fe)2O3 je ostvarena korińćenjem koloidnog kristalnog ńablona – poli(metil metakrilata), i pokazala se pogodnom za dobijanje materijala koji je makroporozan, velikog kapaciteta adsorpcije prema jonima metala, pri ĉemu je uloga sfernih ĉestica poli(metil metakrilata) bila kljuĉna za formiranje makro–pora. Hidroksiapatit je deponovan na Sa, metodom naizmeniĉne jonske adsorpcije i reakcije (SILAR metoda), kojom je postignuta kontrolisana brzina rasta kristala. Nanońenjm apatita u 15, 25 ili 30 ciklusa po 5 s natapanja u svakom prekursoru, sa ispiranjem vodom izmeĊu ciklusa, formiran je relativno uniforman i homogen HAp film na povrńini nosaĉa, sastavljen od agregata finih ĉestica, ńto je rezultiralo hrapavom povrńinom i poroznom strukturom. Povećanjem broja ciklusa koliĉina deponovanog apatita se povećavala, pa je za dalju karakterizaciju, ispitivanja kinetike i adsorpcije/desorpcije, kao najoptimalniji korińćen Sa–HAp sintetisan u 25 ciklusa. Morfologija polaznih i sintetisanih materijala ispitana je skenirajućom elektronskom mikroskopijom (SEM), teksturalna svojstva adsorpcijom azota na temperaturi teĉnog azota (BET metoda), hemijski sastav energetskom disperzionom spektroskopijom (EDS), a vrste veza infracrvenom spektroskopijom sa Furijeovom transformacijom (FTIR). Taĉka nultog naelektrisanja je odreĊena uravnoteņavanjem posebnih proba. Kinetika adsorpcije jona na svim ispitivanim materijalima se bolje opisuje modelom pseudo–drugog reda nego modelima pseudo–prvog i prvog reda, ńto ukazuje na uspostavljanje hemijskih interakcija izmeĊu adsorbata i slobodnih mesta na povrńini adsorbenata. Veber–Morisov kinetiĉki model je pokazao da brzinu adsorpcije odreĊuju i intraĉestiĉna difuzija i difuzija kroz graniĉni sloj. Proces adsorpcije se u sluĉaju Su, Sa i Sa–HAp najbolje opisuje Langmirovim modelom, ńto ukazuje da dolazi do monoslojne adsorpcije. Adsorpcioni kapaciteti Sa–HAp pri svim ispitivanim temperaturama su bili veći u odnosu na adsorpcione kapacitete Sa i Su. Pretpostavlja se da je deponovanje HAp–a na Sa dovelo do povećanja broja hidroksilnih grupa, ńto je pored postojećih amino grupa u Sa, uvedenih zahvaljujući alkalnom tretmanu, dodatno doprinelo većem adsorpcionom kapacitetu Sa–HAp u odnosu na Sa i Su. Proces adsorpcije se u sluĉaju (Al,Fe)2O3, (Al,Fe)2O3APTES i SaCPC–(Al,Fe)2O3APTES najbolje opisuje Frojndlihovim modelom, odnosno adsorpcija je vińeslojna sa heterogenom raspodelom aktivnih centara na povrńini materijala. Adsorpcioni kapaciteti SaCPC– (Al,Fe)2O3APTES pri svim ispitivanim temperaturama su bili veći u odnosu na adsorpcione kapacitete Sa i (Al,Fe)2O3APTES. Iako povrńinska modifikacija aminosilanom ((Al,Fe)2O3APTES) nije dovela do povećanja specifiĉne povrńine, u odnosu na strukturno modifikovan materijal ((Al,Fe)2O3), veći adsorpcioni kapaciteti aminofunkcionalizovanog materijala su posledica funkcionalnosti povrńine. Adsorpcioni kapaciteti hibridnih materiala SaCPC–(Al,Fe)2O3APTES i Sa–HAp za Pb2+, Cd2+ i Ni2+ na poĉetnoj pH = 6, odnosno 6,5 su veći od kapaciteta polaznih materijala (Su, Sa, (Al,Fe)2O3 i (Al,Fe)2O3APTES) zahvaljujući manjem stepenu aglomeracije i time većoj dostupnosti povrńine. Za sve jone i ispitivane materijale povińenje temperature dovodi do povećanja adsorpcionog kapaciteta, ńto ukazuje da je proces adsorpcije endoterman.

The aim of this study was to investigate the influence of modification of alkali–activated subgleba of the mosaic puffball mushroom (Handkea utriformis) using alumina and hydroxyapatite (HAp) on the adsorption of Pb2+, Cd2+ and Ni2+ ions on the obtained materials compared to adsorption on starting materials. These materials were chosen because of their non–toxicity, low cost, chemical and thermal stability, insolubility in water, as well as possibility of obtaining from natural sources and waste. Previous research showed that γ–alumina (γ–Al2O3) and HAp, in different forms, have an affinity for the adsorption of metal ions from aqueous solutions. However, a great tendency towards agglomeration of very fine particles leads to the formation of aggregates, reducing the area available for adsorption and thus their adsorption capacity. To prevent the formation of aggregates and increase the adsorption capacity, alkali–activated subgleba was used as a substrate for deposition of HAp and material based on γ–Al2O3. The porosity and number of surface functional groups (amino and hydroxyl) of the subgleba (Su) are increased by alkaline activation (Sa). Chemical analysis of subgleba confirmed the presence of polysaccharides and proteins, i.e. functional groups suitable for adsorption of metal cations from water, but also for further modification to obtain materials with better adsorption properties. The improvement of the adsorption properties of alumina was achieved by the synthesis of three–dimensionally ordered macroporous (3DOM) alumina doped with iron (III)–oxide, (Al, Fe)2O3, and subsequently surface modified with amino silane (Al,Fe)2O3APTES. Amino groups introduced by surface modification had an additional impact on improving the adsorption properties according to the tested cations, but also achieved the possibility of covalent binding to the alkali– activated surface of the subgleba via 3–(carbomethoxy)propanoyl chloride (CPC), (SaCPC– (Al,Fe)2O3APTES). The synthesis of 3DOM (Al,Fe)2O3 was achieved using a colloidal crystal template – poly(methylmethacrylate) and this method was appropriate to obtain a macroporous material with a high adsorption capacity toward metal ions, while the role of spherical particles of poly(methylmethacrylate) was crucial for the formation of macropores. Alkali treated subglebal material (Sa) was used as a substrate for the deposition of hydroxyapatite by the successive ionic layer adsorption and reaction (SILAR) method that achieved a controlled crystals growth rate. A relatively uniform and homogeneous HAp film, composed of aggregated fine particles, was formed on the substrate surface in 15, 25 or 30 cycles by immersing in each precursor for 5 s and rinsing with water between cycles, providing a rough surface and porous structure. Since the amount of deposited apatite increased with the increasing number of cycles, for further characterization, kinetics and adsorption/desorption tests, Sa–HAp synthesized in 25 cycles was used as the most optimal. The morphology of the starting and synthesized materials was examined using scanning electron microscopy (SEM), textural properties by nitrogen adsorption/desorption isotherms at the temperature of liquid nitrogen (BET method), chemical composition was determined using the energy dispersive spectroscopy (EDS), types of bonds were determined using Fourier–transform infrared spectroscopy (FTIR). The point of zero charge was determined using the pH drift method. The kinetic study of ion adsorption of all tested materials showed that pseudo–second order was the model that best described the experimental adsorption data compared to pseudo first and first order models, indicating the formation of chemical interactions between adsorbates and free sites on the adsorbent surface. The Weber–Morris kinetic model showed that the rate of adsorption is determined by both intraparticle diffusion and boundary layer diffusion. The adsorption process of Su, Sa and Sa–HAp was better described by the Langmuir model, indicating that monolayer adsorption occurs. The adsorption capacities of Sa–HAp, at all examined temperatures, were higher than the adsorption capacities of Sa and Su. It is assumed that the deposition of HAp on Sa led to an increased number of hydroxyl groups, which in addition to the existing amino groups in Sa, introduced due to alkaline treatment, provided the higher adsorption capacity of Sa–HAp compared to Sa and Su. The adsorption on (Al,Fe)2O3, (Al,Fe)2O3APTES and SaCPC–(Al,Fe)2O3APTES was better described by the Freundlich model, i.e. adsorption is multilayered with heterogeneous distribution of active sites on the material surface. The adsorption capacities of SaCPC–(Al,Fe)2O3APTES, at all examined temperatures, were higher than the adsorption capacities of Sa and (Al,Fe)2O3APTES. Although surface modification with amino silane ((Al,Fe)2O3APTES) did not increase specific surface area compared to structurally modified material (Al,Fe)2O3, higher adsorption capacities of amino–functionalized material are a consequence of surface functionality. The capacities of the hybrid materials SaCPC–(Al,Fe)2O3APTES and Sa–HAp for Pb2+, Cd2+ and Ni2+, at the initial pH = 6 or 6.5, are higher than the capacities of the starting materials (Su, Sa, (Al,Fe)2O3 and (Al,Fe)2O3APTES) due to lower degree of agglomeration and thus greater surface availability. For all ions and tested materials, the increase in temperature leads to an increase in the adsorption capacity, which indicates that the adsorption process is endothermic.