A bio-based alginate aerogel as an ionic liquid support for the efficient synthesis of cyclic carbonates from CO2 and epoxides

ca alys s A icle A Bio-Based Algina e Ae ogel as an Ionic Liquid Suppo o he E icien Syn hesis o Cyclic Ca bona es om CO2 and Epoxides Ana B. Paninho 1,2, Ana N. Mus apa 2,3, Kam an T. Mahmudo 4, A mando J. L. Pombei o 4, M. Fá ima C. Guedes da Sil a 4, Ma ía D. Be mejo 2,Ángel Ma ín2, Ma ía J. Coce o 2and Ana V. M. Nunes 1,*   Ci a ion: Paninho, A.B.; Mus apa, A.N.; Mahmudo , K.T.; Pombei o, A.J.L.; Guedes da Sil a, M.F.C.; Be mejo, M.D.; Ma ín, Á.; Coce o, M.J.; Nunes, A.V.M. A Bio-Based Algina e Ae ogel as an Ionic Liquid Suppo o he E icien Syn hesis o Cyclic Ca bona es om CO2and Epoxides. Ca alys s 2021,11, 872. h ps://doi.o g/10.3390/ca al11080872 Academic Edi o : Ca ia Cannilla Recei ed: 9 June 2021 Accep ed: 9 July 2021 Published: 21 July 2021 Publishe ’s No e: MDPI s ays neu al wi h ega d o ju isdic ional claims in published maps and ins i u ional a il- ia ions. Copy igh : © 2021 by he au ho s. Licensee MDPI, Basel, Swi ze land. This a icle is an open access a icle dis ibu ed unde he e ms and condi ions o he C ea i e Commons A ibu ion (CC BY) license (h ps:// c ea i ecommons.o g/licenses/by/ 4.0/). 1 LAQV, REQUIMTE, Depa amen o de Química, Faculdade de Ciências e Tecnologia, Uni e sidade No a de Lisboa, 2829-516 Capa ica, Po ugal; [email p o ec ed] 2High P essu e P ocesses G oup, Indus ial Enginee ing School, Depa men o Chemical Enginee ing and En i onmen al Technology, Uni e si y o Valladolid, C/D . Me gelina, s/n, 47011 Valladolid, Spain; [email p o ec ed] (A.N.M.); [email p o ec ed] (M.D.B.); [email p o ec ed] (Á.M.); [email p o ec ed] (M.J.C.) 3School o Chemical Enginee ing, College o Enginee ing, Uni e si i Teknologi MARA (UiTM), Shah Alam 40450, Selango , Malaysia 4Cen o de Química Es u u al, Ins i u o Supe io Técnico, Uni e sidade de Lisboa, A . Ro isco Pais, 1049-001 Lisbon, Po ugal; [email p o ec ed] (K.T.M.); [email p o ec ed] (A.J.L.P.); [email p o ec ed] (M.F.C.G.d.S.) *Co espondence: [email p o ec ed] Abs ac : In his wo k, he ionic liquid [Aliqua ][Cl] was suppo ed in o algina e and silica ae ogel ma ices and applied as a ca alys in he cycloaddi ion eac ion be ween CO 2 and a bio-based epoxide (limonene oxide). The e iciency o he algina e ae ogel sys em is much highe han ha o he silica one. The me hod o we imp egna ion was used o he imp egna ion o he ae ogel wi h [Aliqua ][Cl] and a zinc complex. The p ocedu e o igina ed a well-de ined hin sol en ilm on he su ace o suppo ma e ials. Final ma e ials we e cha ac e ised by Fou ie T ans o m In a ed Spec oscopy, N 2 Adso p ion–Deso p ion Analysis, X- ay di ac ion, a omic abso p ion and Field Emission Scanning Mic oscopy. Se e al ca aly ic es s we e pe o med in a high-p essu e appa a us a 353.2 K and 4 MPa o CO2. Keywo ds: cyclic ca bona es; CO 2 ; epoxides; cycloaddi ion; algina e ae ogels; supe c i ical; sup- po ed ionic liquids; limonene ca bona e 1. In oduc ion The u iliza ion o CO 2 as s a ing ma e ial o p oduce cyclic ca bona es is a e y ac i e ield o esea ch. Cyclic ca bona es a e pa icula ly a ac i e as in e media e CO 2 de i a i es since hey can be o med eadily om he ca aly ic coupling eac ion be ween CO 2 and he co esponding epoxide [ 1 – 3 ]. Fu he mo e, cyclic ca bona es a e b oadly used as pola ap o ic sol en s, uel addi i es, elec oly es o li hium-ion ba e ies, ine chemicals in e media es as well as monome s in polyme iza ion eac ions [ 4 ]. Bina y ca aly ic sys ems composed o homogeneous me al complexes oge he wi h ionic liquids ha e been success ully used [ 5 – 7 ]. Se e al mechanis ic s udies showed ha he ionic liquid plays a c ucial ole in he eac ion kine ics, wi h he anion being esponsible o he nucleophilic a ack o he epoxide ing, which is he a e-de e mining s ep [ 8 – 11 ]. Recen ly, [Aliqua ][Cl] was used bo h as ca alys and sol en in he cycloaddi ion eac ion be ween CO2and p opylene oxide a high p essu es [12]. The combina ion o high-p essu e CO 2 wi h ionic liquids o igina es an e icien bipha- sic sys em o ca y ou liquid phase ca alysis. The ac ha ionic liquids a e p ac ically insoluble in CO 2 , while CO 2 p esen s high solubili y in se e al ypes o hese o ganic sal s, Ca alys s 2021,11, 872. h ps://doi.o g/10.3390/ca al11080872 h ps://www.mdpi.com/jou nal/ca alys s Ca alys s 2021,11, 872 2 o 16 allows o use CO 2 as a mobile phase o anspo eac an s in and ou o he ionic liquid phase, whe e homogeneous ca alys s a e dissol ed [ 13 ]. Fu he mo e, besides negligible apou p essu e, one o he mos ema kable ea u es o ionic liquids is hei uneable sol- en powe , h ough he possibili y o “design” i s physicochemical p ope ies by changing he anion/ca ion pai [14]. In his con ex , se e al au ho s ha e explo ed hei u iliza ion co alen ly a ached o physically adso bed on o solid ma e ials sui able o ixed bed ope a ions [ 15 ]. This app oach is also known as Suppo ed Ionic Liquid Phase (SILP) ca alysis [ 16 ]. The concep in ol es dissol ing a homogeneous ca alys in an ionic liquid ha is u he immobilized on he su ace o a solid suppo , b inging oge he ad an ages o bo h homogeneous (high a es and good selec i i y) and he e ogeneous ca alysis (easy sepa a ion, ecyclabili y and con inuous ope a ion) [ 17 ]. Fu he mo e, SILP ca alysis allows he usage o signi ican ly lowe amoun s o ionic liquid, conside able educing he di usion pa hway when com- pa ed o bulk biphasic sys ems, a oiding mass anspo limi a ions and he eby leading o high eac ion a es [ 18 ]. O e he las decade, SILPs ha e been used as unc ional ma e ials and media, namely in ca alysis and elec ochemis y, in sepa a ion p ocesses and as su ace modi ying agen s [19]. Rega ding SILP p epa a ion me hods, he ionic liquid can be chemically bond o simply physically adso bed on he su ace o a po ous suppo ma e ial. When he ionic liquid is co alen ly bound o he suppo , he chemical bonding may limi he deg ee o eedom o he ca ion/anion o e en change some p ope ies o he ionic liquid as i s sol a ion s eng h. Ne e heless, a no o ious ad an age is he minimiza ion (o e en elimina ion) o he highly undesi able phenomena o leakage o he ionic liquid laye in o he eac ion mix u e. On he o he hand, when a laye o ionic liquid is adso bed a he su ace o a po ous suppo ma e ial, i is possible o ake ad an age o ull bulk p ope ies o he ionic liquid. Physiso p ion s ands as he mos simple and s aigh o wa d me hod o p epa a ion, bu he ionic liquid is mo e suscep ible o leaching du ing he ca aly ic p ocess, especially when pola subs a es a e used. Tha ’s he eason why, in p ac ice, applica ions o physical adso bed SILP ma e ials a e mos ly limi ed o gas-phase ope a ions. Addi ionally, a a ie y o suppo ma e ials [ 20 ] has been used, as g aphene oxide [ 21 ], alumina [ 22 ], i ania [ 22 ], molecula sie es [ 23 ], me al o ganic amewo ks (MOFs) [ 24 ], o ganic polyme s [ 25 ] and poly-ionic liquids [ 26 , 27 ]. Silica is by a he mos explo ed ma e ial o he cycloaddi ion eac ion be ween CO 2 and epoxides [ 28 – 32 ]. Sakaku a and co-wo ke s epo ed ha silica-suppo ed onium sal s achie ed much highe ca aly ic ac i i ies compa ed o onium sal s alone [ 33 ]. In hese eac ions, he coope a i e ac ion o he silanol g oups and he nucleophile a e esponsible o he oxygen a om coo dina ion and he nucleophilic ing opening o he epoxide, espec i ely [ 34 ]. Simila esul s we e epo ed by Takashi Sakai e al. [ 35 ]. In his las wo k, i was also ound ha he po e size o he ma e ial a ec ed he eac ion kine ics, wi h ma e ials bea ing a po e size o 19 nm exhibi ing much be e pe o mance when compa ed o silica ma e ials bea ing a mean po e size o 6 nm. The u iliza ion o biopolyme s as ionic liquids suppo s is a e y a ac i e s a egy since biopolyme sou ces a e well es ablished, a e ela i ely cheap and accessible a indus- ial scale. Howe e , o he bes o ou knowledge, o he cycloaddi ion eac ion be ween CO2and epoxides, hei use is s ill limi ed o cellulose de i a i es and chi osan [36–38]. On he con ex o ou in e es in de eloping g eene app oaches o CO 2 con e sion in o o ganic ca bona es [ 39 ], in his wo k, we ha e suppo ed an ionic liquid ([Aliqua ][Cl]) in o an algina e ae ogel ma ix and applied i as SILP ca alys o he cycloaddi ion eac ion be ween CO 2 and limonene oxide (a bio-based epoxide). The use o epoxides de i ed om enewable esou ces such as was e biomass has ecen ly ecei ed inc easing a en ion as a s a egy o p oduce ully sus ainable cyclic ca bona es [ 40 – 42 ]. In pa icula , limonene epox- ide has been explo ed in se e al s udies as a enewable subs a e ha is also pa icula ly challenging due o in insically highe s e ic demand [43,44]. Ca alys s 2021,11, 872 3 o 16 The biopolyme algina e is na u ally de i ed om he seaweed b own algae and is composed wi h α -L-gulu onic acid and β -D-mannu onic acid blocks, linea ly linked by 1,4-glycosidic linkage. Due o i s biodeg adabili y, low cos , non- oxici y and s abili y, i is an a ac i e candida e o SILP p epa a ion and applica ion in ca bona es p oduc ion [ 45 ]. 2. Resul s and Discussion The p epa a ion and imp egna ion me hods ca ied ou o silica (SIL) and algina e (ALG) ae ogels wi h he zinc complex (Zn) and/o he ionic liquid [Aliqua ][Cl] (IL) a e summa ized in Table 1. The zinc complex used in his wo k was syn hesized and ex ensi ely cha ac e ised in a p e iously wo k [46,47]. Table 1. Imp egna ed silica (SIL) and algina e (ALG) ae ogels p epa ed by he we imp egna ion me hod. Ma ix Ma e ial Re e ence Subs ance Imp egna ed Silica Zn-SIL1 Zn(II)-AHBD Zn-SIL2 Zn(II)-AHBD Zn-IL-SIL2 Zn(II)-AHBD + IL Algina e Zn-ALG Zn(II)-AHBD Zn-IL-ALG Zn(II)-AHBD + IL IL-ALG IL 2.1. In a ed Spec oscopy S udies Figu es 1–3show he esul s o FTIR assays o he imp egna ed algina e and silica ae ogels in compa ison wi h blank ae ogels, pu e Zn(II)-AHBD ca alys and pu e [Ali- qua ][Cl]. The y-axis scale is he same o all cu es. The co esponding abso p ion bands o he Zn(II)-AHBD ca alys we e no obse ed clea ly in he imp egna ed samples, which can indica e ha only a low amoun was imp egna ed in o he ae ogels. Fo he blank algina e ae ogel (Figu e 1, ALG), i is possible o obse e se e al cha ac e is ic abso p ion bands a 3450 cm−1(O-H s e ching) and he alginic acid bands be ween 700 and 1800 cm−1[48]. Ca alys s 2021, 11, x FOR PEER REVIEW 3 o 16 pa icula , limonene epoxide has been explo ed in se e al s udies as a enewable subs a e ha is also pa icula ly challenging due o in insically highe s e ic demand [43,44]. The biopolyme algina e is na u ally de i ed om he seaweed b own algae and is composed wi h α-L-gulu onic acid and β-D-mannu onic acid blocks, linea ly linked by 1,4-glycosidic linkage. Due o i s biodeg adabili y, low cos , non- oxici y and s abili y, i is an a ac i e candida e o SILP p epa a ion and applica ion in ca bona es p oduc ion [45]. 2. Resul s and Discussion The p epa a ion and imp egna ion me hods ca ied ou o silica (SIL) and algina e (ALG) ae ogels wi h he zinc complex (Zn) and/o he ionic liquid [Aliqua ][Cl] (IL) a e summa ized in Table 1. The zinc complex used in his wo k was syn hesized and ex en- si ely cha ac e ised in a p e iously wo k [46,47]. Table 1. Imp egna ed silica (SIL) and algina e (ALG) ae ogels p epa ed by he we imp egna ion me hod. Ma ix Ma e ial Re e ence Subs ance Imp egna ed Silica Zn-SIL1 Zn(II)-AHBD Zn-SIL2 Zn(II)-AHBD Zn-IL-SIL2 Zn(II)-AHBD + IL Algina e Zn-ALG Zn(II)-AHBD Zn-IL-ALG Zn(II)-AHBD + IL IL-ALG IL 2.1. In a ed Spec oscopy S udies Figu es 1–3 show he esul s o FTIR assays o he imp egna ed algina e and silica ae ogels in compa ison wi h blank ae ogels, pu e Zn(II)-AHBD ca alys and pu e [Ali- qua ][Cl]. The y-axis scale is he same o all cu es. The co esponding abso p ion bands o he Zn(II)-AHBD ca alys we e no obse ed clea ly in he imp egna ed samples, which can indica e ha only a low amoun was imp egna ed in o he ae ogels. Fo he blank algina e ae ogel (Figu e 1, ALG), i is possible o obse e se e al cha ac e is ic abso p ion bands a 3450 cm−1 (O-H s e ching) and he alginic acid bands be ween 700 and 1800 cm−1 [48]. Figu e 1. In a ed spec a o pu e Zn(II)-AHBD ca alys (Zn), pu e [Aliqua ][Cl] (IL) and algina e ae ogels: blank algina e ae ogel (ALG), Zn(II)-AHBD-imp egna ed ae ogel (Zn-ALG), ae ogel im- p egna ed wi h Zn(II)-AHBD and [Aliqua ][Cl] (Zn-IL-ALG) and ae ogel imp egna ed wi h [Ali- qua ][Cl] (IL-ALG). Figu e 1. In a ed spec a o pu e Zn(II)-AHBD ca alys (Zn), pu e [Aliqua ][Cl] (IL) and algina e ae ogels: blank algina e ae ogel (ALG), Zn(II)-AHBD-imp egna ed ae ogel (Zn-ALG), ae ogel imp eg- na ed wi h Zn(II)-AHBD and [Aliqua ][Cl] (Zn-IL-ALG) and ae ogel imp egna ed wi h [Aliqua ][Cl] (IL-ALG). The co esponding abso p ion bands o pu e [Aliqua ][Cl] (Figu e 1, IL) can be seen a 1480 cm −1 (CH2 blending) and be ween 2800 and 3000 cm −1 (C-H s e ching) [ 49 ]. The ob ained spec um o pu e [Aliqua ][Cl] was compa ed wi h he [Aliqua ][Cl]-imp egna ed algina e ae ogels (Figu e 1, Zn-IL-ALG and IL-ALG) and i was obse ed ha [Aliqua ][Cl] Ca alys s 2021,11, 872 4 o 16 cha ac e is ic peaks also appea ed in he spec um, which indica es ha [Aliqua ][Cl] was success ully imp egna ed in o he algina e ae ogels. A simila beha iou o he Zn(II)- AHBD + [Aliqua ][Cl]-imp egna ed silica ae ogels was obse ed, as shown in Figu e 2 (Silica SIL2). In his case, i was also possible o obse e he [Aliqua ][Cl] cha ac e is ic peaks in he spec um. In compa ison wi h algina e ae ogel, he silica ae ogel SIL2 had weake abso p ion bands a 1480 cm −1 and be ween 2800 and 3000 cm −1 , which indica es a lowe [Aliqua ][Cl] loading. Fo he sample Silica SIL1 (Figu e 3), he cha ac e is ic peaks o he Zn(II)-AHBD ca alys we e no obse ed, which may indica e ha his imp egna ion was no so success ul as he p e ious ones. Fu he mo e, silica ae ogels p esen ed a highly agile s uc u e and we e no used in high p essu e ca aly ic es s. Ca alys s 2021, 11, x FOR PEER REVIEW 4 o 16 The co esponding abso p ion bands o pu e [Aliqua ][Cl] (Figu e 1, IL) can be seen a 1480 cm−1 (CH2 blending) and be ween 2800 and 3000 cm−1 (C-H s e ching) [49]. The ob ained spec um o pu e [Aliqua ][Cl] was compa ed wi h he [Aliqua ][Cl]-imp eg- na ed algina e ae ogels (Figu e 1, Zn-IL-ALG and IL-ALG) and i was obse ed ha [Ali- qua ][Cl] cha ac e is ic peaks also appea ed in he spec um, which indica es ha [Ali- qua ][Cl] was success ully imp egna ed in o he algina e ae ogels. A simila beha iou o he Zn(II)-AHBD + [Aliqua ][Cl]-imp egna ed silica ae ogels was obse ed, as shown in Figu e 2 (Silica SIL2). Figu e 2. In a ed spec a o pu e Zn(II)-AHBD ca alys (Zn), pu e [Aliqua ][Cl] (IL) and silica ae - ogels: blank silica ae ogel (SIL2), Zn(II)-AHBD-imp egna ed ae ogel (Zn-SIL2) and ae ogel imp eg- na ed wi h Zn(II)-AHBD and [Aliqua ][Cl] (Zn-IL-SIL2). In his case, i was also possible o obse e he [Aliqua ][Cl] cha ac e is ic peaks in he spec um. In compa ison wi h algina e ae ogel, he silica ae ogel SIL2 had weake ab- so p ion bands a 1480 cm−1 and be ween 2800 and 3000 cm−1, which indica es a lowe [Aliqua ][Cl] loading. Fo he sample Silica SIL1 (Figu e 3), he cha ac e is ic peaks o he Zn(II)-AHBD ca alys we e no obse ed, which may indica e ha his imp egna ion was no so success ul as he p e ious ones. Fu he mo e, silica ae ogels p esen ed a highly agile s uc u e and we e no used in high p essu e ca aly ic es s. Figu e 3. In a ed spec a o pu e Zn(II)-AHBD ca alys (Zn) and silica ae ogels: blank silica ae ogel (SIL1) and Zn(II)-AHBD-imp egna ed ae ogel (Zn-SIL1). F om he FTIR esul s p esen ed in Figu e 3, he Zn(II)-AHBD imp egna ion e i- ciency was di icul o e alua e. In ac , due o he complexi y o he ca alys s uc u e (Figu e 4), he abso p ion bands appea o e lapping and less de ined. This hampe s he FTIR analysis o Zn(II)-AHBD con en in he ae ogels and p omp ed us o use a omic ab- so p ion echnique. Figu e 2. In a ed spec a o pu e Zn(II)-AHBD ca alys (Zn), pu e [Aliqua ][Cl] (IL) and silica ae ogels: blank silica ae ogel (SIL2), Zn(II)-AHBD-imp egna ed ae ogel (Zn-SIL2) and ae ogel im- p egna ed wi h Zn(II)-AHBD and [Aliqua ][Cl] (Zn-IL-SIL2). Ca alys s 2021, 11, x FOR PEER REVIEW 4 o 16 The co esponding abso p ion bands o pu e [Aliqua ][Cl] (Figu e 1, IL) can be seen a 1480 cm−1 (CH2 blending) and be ween 2800 and 3000 cm−1 (C-H s e ching) [49]. The ob ained spec um o pu e [Aliqua ][Cl] was compa ed wi h he [Aliqua ][Cl]-imp eg- na ed algina e ae ogels (Figu e 1, Zn-IL-ALG and IL-ALG) and i was obse ed ha [Ali- qua ][Cl] cha ac e is ic peaks also appea ed in he spec um, which indica es ha [Ali- qua ][Cl] was success ully imp egna ed in o he algina e ae ogels. A simila beha iou o he Zn(II)-AHBD + [Aliqua ][Cl]-imp egna ed silica ae ogels was obse ed, as shown in Figu e 2 (Silica SIL2). Figu e 2. In a ed spec a o pu e Zn(II)-AHBD ca alys (Zn), pu e [Aliqua ][Cl] (IL) and silica ae - ogels: blank silica ae ogel (SIL2), Zn(II)-AHBD-imp egna ed ae ogel (Zn-SIL2) and ae ogel imp eg- na ed wi h Zn(II)-AHBD and [Aliqua ][Cl] (Zn-IL-SIL2). In his case, i was also possible o obse e he [Aliqua ][Cl] cha ac e is ic peaks in he spec um. In compa ison wi h algina e ae ogel, he silica ae ogel SIL2 had weake ab- so p ion bands a 1480 cm−1 and be ween 2800 and 3000 cm−1, which indica es a lowe [Aliqua ][Cl] loading. Fo he sample Silica SIL1 (Figu e 3), he cha ac e is ic peaks o he Zn(II)-AHBD ca alys we e no obse ed, which may indica e ha his imp egna ion was no so success ul as he p e ious ones. Fu he mo e, silica ae ogels p esen ed a highly agile s uc u e and we e no used in high p essu e ca aly ic es s. Figu e 3. In a ed spec a o pu e Zn(II)-AHBD ca alys (Zn) and silica ae ogels: blank silica ae ogel (SIL1) and Zn(II)-AHBD-imp egna ed ae ogel (Zn-SIL1). F om he FTIR esul s p esen ed in Figu e 3, he Zn(II)-AHBD imp egna ion e i- ciency was di icul o e alua e. In ac , due o he complexi y o he ca alys s uc u e (Figu e 4), he abso p ion bands appea o e lapping and less de ined. This hampe s he FTIR analysis o Zn(II)-AHBD con en in he ae ogels and p omp ed us o use a omic ab- so p ion echnique. Figu e 3. In a ed spec a o pu e Zn(II)-AHBD ca alys (Zn) and silica ae ogels: blank silica ae ogel (SIL1) and Zn(II)-AHBD-imp egna ed ae ogel (Zn-SIL1). F om he FTIR esul s p esen ed in Figu e 3, he Zn(II)-AHBD imp egna ion e i- ciency was di icul o e alua e. In ac , due o he complexi y o he ca alys s uc u e ( Figu e 4 ), he abso p ion bands appea o e lapping and less de ined. This hampe s he FTIR analysis o Zn(II)-AHBD con en in he ae ogels and p omp ed us o use a omic abso p ion echnique. Ca alys s 2021,11, 872 5 o 16 Ca alys s 2021, 11, x FOR PEER REVIEW 5 o 16 Figu e 4. Zn(II)-AHBD ca alys (zinc(II) complex o an a ylhyd azone o a β-dike one). 2.2. Ni ogen Physiso p ion S udies Table 2 shows he ex u al p ope ies o blank and imp egna ed algina e and silica ae ogels. Rega ding esul s ob ained o blank ae ogels (no imp egna ed), i was possible o obse e ha silica ae ogels p esen ed a highe su ace a ea and lowe po e diame e han algina e ae ogels, which is in acco dance wi h esul s epo ed by o he au ho s [50]. This di e ence in po es diame e is ega ded as he basis o a lowe imp egna ion e i- ciency in o silica ma ices [35]. Table 2. Tex u al p ope ies o blank and imp egna ed silica (SIL) and algina e (ALG) ae ogels. Ae ogels we e imp eg- na ed wi h he zinc complex (Zn) and/o he ionic liquid [Aliqua ][Cl] (IL). Ma ix Ae ogel Re e ence Imp egna ion a SBET (m2/g) Po e Volume (cm3/g) Po e Diame e (nm) Silica SIL1 - 882 2.85 12.93 Zn-SIL1 Zn(II)-AHBD 772 2.96 15.35 SIL2 - 1099 2.44 8.91 Zn-SIL2 Zn(II)-AHBD 258 0.475 7.36 Zn-IL-SIL2 Zn(II)-AHBD + IL 245 0.445 7.25 Algina e ALG - 271 2.27 33.56 Zn-ALG Zn(II)-AHBD 253 2.18 34.46 Zn-IL-ALG Zn(II)-AHBD + IL <1 - - IL-ALG IL <1 - - a The ionic liquid used o imp egna ion was always [Aliqua ][Cl]. When he ae ogels we e imp egna ed wi h Zn(II)-AHBD, a dec ease (usually sligh bu p onounced in he case o SIL2) o he speci ic su ace a ea was obse ed. On he o he hand, when imp egna ed wi h he ionic liquid ([Aliqua ][Cl]), which is an o ganic sal liquid a oom empe a u e, he ae ogel po es we e o ally illed, wi h consequen d as ic dec ease in he su ace a eas and po e olumes. This e ec is mo e p onounced o algi- na e ae ogels, especially he ones ha we e imp egna ed wi h [Aliqua ][Cl], o which he BET su ace a ea esul s we e always lowe han 1 m2/g. Also, he algina e ae ogel imp eg- na ed wi h bo h [Aliqua ][Cl] and Zn(II)-AHBD p esen ed a BET su ace a ea lowe han 1 m2/g. In he case o silica ae ogels his e ec was no so e iden , e y likely due o he ac ha he imp egna ion was less e icien . As a complemen o he esul s epo ed in he Table 2, Figu e 5 shows he ni ogen adso p ion iso he ms o he blank and imp egna e algina e and silica ae ogels. The iso he ms belong o “ ype IV” which is ypical o meso- po ous ma e ials. When he imp egna ion was pe o med wi h [Aliqua ][Cl] (Zn-IL-ALG and IL-ALG, Figu e 5) he e is no deso p ion o N2 om he ae ogels, which is in acco d- ance wi h he BET su ace esul s. Figu e 4. Zn(II)-AHBD ca alys (zinc(II) complex o an a ylhyd azone o a β-dike one). 2.2. Ni ogen Physiso p ion S udies Table 2shows he ex u al p ope ies o blank and imp egna ed algina e and silica ae ogels. Rega ding esul s ob ained o blank ae ogels (no imp egna ed), i was possible o obse e ha silica ae ogels p esen ed a highe su ace a ea and lowe po e diame e han algina e ae ogels, which is in acco dance wi h esul s epo ed by o he au ho s [ 50 ]. This di e ence in po es diame e is ega ded as he basis o a lowe imp egna ion e iciency in o silica ma ices [35]. Table 2. Tex u al p ope ies o blank and imp egna ed silica (SIL) and algina e (ALG) ae ogels. Ae ogels we e imp egna ed wi h he zinc complex (Zn) and/o he ionic liquid [Aliqua ][Cl] (IL). Ma ix Ae ogel Re e ence Imp egna ion aSBET (m2/g) Po e Volume (cm3/g) Po e Diame e (nm) Silica SIL1 - 882 2.85 12.93 Zn-SIL1 Zn(II)-AHBD 772 2.96 15.35 SIL2 - 1099 2.44 8.91 Zn-SIL2 Zn(II)-AHBD 258 0.475 7.36 Zn-IL-SIL2 Zn(II)-AHBD + IL 245 0.445 7.25 Algina e ALG - 271 2.27 33.56 Zn-ALG Zn(II)-AHBD 253 2.18 34.46 Zn-IL-ALG Zn(II)-AHBD + IL <1 - - IL-ALG IL <1 - - aThe ionic liquid used o imp egna ion was always [Aliqua ][Cl]. When he ae ogels we e imp egna ed wi h Zn(II)-AHBD, a dec ease (usually sligh bu p onounced in he case o SIL2) o he speci ic su ace a ea was obse ed. On he o he hand, when imp egna ed wi h he ionic liquid ([Aliqua ][Cl]), which is an o ganic sal liquid a oom empe a u e, he ae ogel po es we e o ally illed, wi h consequen d as ic dec ease in he su ace a eas and po e olumes. This e ec is mo e p onounced o algina e ae ogels, especially he ones ha we e imp egna ed wi h [Aliqua ][Cl], o which he BET su ace a ea esul s we e always lowe han 1 m 2 /g. Also, he algina e ae ogel imp egna ed wi h bo h [Aliqua ][Cl] and Zn(II)-AHBD p esen ed a BET su ace a ea lowe han 1 m 2 /g. In he case o silica ae ogels his e ec was no so e iden , e y likely due o he ac ha he imp egna ion was less e icien . As a complemen o he esul s epo ed in he Table 2, Figu e 5shows he ni ogen adso p ion iso he ms o he blank and imp egna e algina e and silica ae ogels. The iso he ms belong o “ ype IV” which is ypical o mesopo ous ma e ials. When he imp egna ion was pe o med wi h [Aliqua ][Cl] (Zn-IL-ALG and IL-ALG, Figu e 5) he e is no deso p ion o N2 om he ae ogels, which is in acco dance wi h he BET su ace esul s. Ca alys s 2021,11, 872 6 o 16 Ca alys s 2021, 11, x FOR PEER REVIEW 6 o 16 Figu e 5. Ni ogen adso p ion iso he ms o he algina e and silica ae ogels. 2.3. Powde X- ay Di ac ion S udies X- ay di ac ion pa e ns o silica and algina e ae ogels a e shown in he Figu es 6 and 7, espec i ely. Since his echnique de ec s he c ys allini y o he imp egna ed Zn(II)- AHBD pa icles, he ae ogels con aining only [Aliqua ][Cl] we e no analysed by his ech- nique. The X- ay di ac ion pa e ns o blank silica ae ogels (SIL1 and SIL2) and Zn(II)- AHBD imp egna ed silica ae ogels (Zn-SIL1 and Zn-SIL2) a e ep esen ed in he Figu e 6. No changes on c ys allini y o imp egna ed silica ae ogels we e obse ed. The e o e, he discussions on he e ec o imp egna ion on su ace mo phology will be ocused only in he algina e ae ogels Figu e 6. X- ay di ac ion pa e ns o Zn(II)-AHBD-imp egna ed silica ae ogels and blank silica ae ogels. The di ac og am o algina e is known o consis o wo c ys alline peaks a ound 14 and 23° o 2θ which a e ela ed o he la e al packing among molecula chains and he laye spacing along he molecula chain di ec ion, espec i ely [51,52]. Fo he blank algi- na e ae ogel (Figu e 7, ALG) i was possible o obse e se e al cha ac e is ic di ac ion peaks; he mos in ense a e 23.3°, 29.6°, 35.9°, 39.4°, 42.9°, 47.1° and 48.4°. The e a e wo e iden ypical di ac ion peaks o pu e Zn(II)-AHBD ca alys (Figu e 7, Zn) ha can be de ec ed a 7.7° and 25.1°. The spec um o pu e Zn(II)-AHBD was compa ed wi h hose o he imp egna ed ae ogels (Figu e 7, Zn-ALG) and i was possible o obse e ha he 10 30 50 70 2θ(o) Zn-SIL1 SIL1 Zn-IL-SIL2 Zn-SIL2 SIL2 Figu e 5. Ni ogen adso p ion iso he ms o he algina e and silica ae ogels. 2.3. Powde X- ay Di ac ion S udies X- ay di ac ion pa e ns o silica and algina e ae ogels a e shown in he Figu es 6and 7 , espec i ely. Since his echnique de ec s he c ys allini y o he imp eg- na ed Zn(II)-AHBD pa icles, he ae ogels con aining only [Aliqua ][Cl] we e no analysed by his echnique. The X- ay di ac ion pa e ns o blank silica ae ogels (SIL1 and SIL2) and Zn(II)-AHBD imp egna ed silica ae ogels (Zn-SIL1 and Zn-SIL2) a e ep esen ed in he Figu e 6. No changes on c ys allini y o imp egna ed silica ae ogels we e obse ed. The e o e, he discussions on he e ec o imp egna ion on su ace mo phology will be ocused only in he algina e ae ogels. Ca alys s 2021, 11, x FOR PEER REVIEW 6 o 16 Figu e 5. Ni ogen adso p ion iso he ms o he algina e and silica ae ogels. 2.3. Powde X- ay Di ac ion S udies X- ay di ac ion pa e ns o silica and algina e ae ogels a e shown in he Figu es 6 and 7, espec i ely. Since his echnique de ec s he c ys allini y o he imp egna ed Zn(II)- AHBD pa icles, he ae ogels con aining only [Aliqua ][Cl] we e no analysed by his ech- nique. The X- ay di ac ion pa e ns o blank silica ae ogels (SIL1 and SIL2) and Zn(II)- AHBD imp egna ed silica ae ogels (Zn-SIL1 and Zn-SIL2) a e ep esen ed in he Figu e 6. No changes on c ys allini y o imp egna ed silica ae ogels we e obse ed. The e o e, he discussions on he e ec o imp egna ion on su ace mo phology will be ocused only in he algina e ae ogels Figu e 6. X- ay di ac ion pa e ns o Zn(II)-AHBD-imp egna ed silica ae ogels and blank silica ae ogels. The di ac og am o algina e is known o consis o wo c ys alline peaks a ound 14 and 23° o 2θ which a e ela ed o he la e al packing among molecula chains and he laye spacing along he molecula chain di ec ion, espec i ely [51,52]. Fo he blank algi- na e ae ogel (Figu e 7, ALG) i was possible o obse e se e al cha ac e is ic di ac ion peaks; he mos in ense a e 23.3°, 29.6°, 35.9°, 39.4°, 42.9°, 47.1° and 48.4°. The e a e wo e iden ypical di ac ion peaks o pu e Zn(II)-AHBD ca alys (Figu e 7, Zn) ha can be de ec ed a 7.7° and 25.1°. The spec um o pu e Zn(II)-AHBD was compa ed wi h hose o he imp egna ed ae ogels (Figu e 7, Zn-ALG) and i was possible o obse e ha he 10 30 50 70 2θ(o) Zn-SIL1 SIL1 Zn-IL-SIL2 Zn-SIL2 SIL2 Figu e 6. X- ay di ac ion pa e ns o Zn(II)-AHBD-imp egna ed silica ae ogels and blank silica ae ogels. The di ac og am o algina e is known o consis o wo c ys alline peaks a ound 14 and 23 ◦ o 2 θ which a e ela ed o he la e al packing among molecula chains and he laye spacing along he molecula chain di ec ion, espec i ely [ 51 , 52 ]. Fo he blank algina e ae ogel (Figu e 7, ALG) i was possible o obse e se e al cha ac e is ic di ac ion peaks; he mos in ense a e 23.3 ◦ , 29.6 ◦ , 35.9 ◦ , 39.4 ◦ , 42.9 ◦ , 47.1 ◦ and 48.4 ◦ . The e a e wo e iden ypical di ac ion peaks o pu e Zn(II)-AHBD ca alys (Figu e 7, Zn) ha can be de ec ed a 7.7 ◦ and 25.1 ◦ . The spec um o pu e Zn(II)-AHBD was compa ed wi h hose o he imp egna ed ae ogels (Figu e 7, Zn-ALG) and i was possible o obse e ha he Zn(II)- AHBD cha ac e is ic peaks appea ed. This esul indica es ha al hough in low amoun s, he Zn(II)-AHBD complex was success ully imp egna ed in o he algina e ae ogels. Ca alys s 2021,11, 872 7 o 16 Ca alys s 2021, 11, x FOR PEER REVIEW 7 o 16 Zn(II)-AHBD cha ac e is ic peaks appea ed. This esul indica es ha al hough in low amoun s, he Zn(II)-AHBD complex was success ully imp egna ed in o he algina e ae o- gels. Figu e 7. X- ay di ac ion pa e ns o Zn(II)-AHBD- and [Aliqua ][Cl]-imp egna ed algina e ae o- gels (Zn-IL-ALG), Zn(II)-AHBD-imp egna ed algina e ae ogels (Zn-ALG), blank algina e ae ogels (ALG) and pu e Zn(II)-AHBD ca alys (Zn), espec i ely. 2.4. Ae ogels Images The images o he imp egna ed algina e and silica ae ogels a e p esen ed in he Fig- u es 8 and 9, espec i ely. Figu e 8 shows images o se e al algina e ae ogels, namely, blank ae ogel sample (a), Zn(II)-AHBD-imp egna ed ae ogel (b), Zn(II)-AHBD+[Ali- qua ][Cl]-imp egna ed ae ogel (c) and ae ogel imp egna ed only wi h [Aliqua ][Cl] (d). Zn(II)-AHBD-imp egna ed ae ogels (Figu e 8b,c) p esen a b own colou , indica ing he p esence o he Zn(II)-AHBD ca alys in he ma ix. The same cha ac e is ics we e ob- se ed o he ex e io and in e io o he imp egna ed ae ogels, indica ing a homogene- ous loading o he whole ae ogel monoli h. [Aliqua ][Cl]-imp egna ed samples (Figu e 8d) p esen ed a yellowish appea ance due o he p esence o he ionic liquid, which con- as ed wi h he blank samples (Figu e 8a). Again, a homogeneous loading o he whole ae ogel monoli h was obse ed. . (a) (b) (c) (d) Figu e 8. Images o algina e ae ogels: algina e ae ogels, (a) blank, (b) Zn(II)-AHBD-imp egna ed, (c) Zn(II)-AHBD + [Aliqua ][Cl]-imp egna ed, (d) [Aliqua ][Cl]-imp egna ed. In Figu e 9a,b a e p esen ed images o he silica ae ogels SIL1 and SIL2. The i s sample is a blank ae ogel, ollowed by a Zn(II)-AHBD imp egna ed ae ogel and in he case o image 11b) also Zn(II)-AHBD+[Aliqua ][Cl] imp egna ed silica ae ogel. 5 10 15 20 25 30 35 40 45 50 55 60 65 70 2θ (º) Zn-IL-ALG Zn-ALG ALG Zn Figu e 7. X- ay di ac ion pa e ns o Zn(II)-AHBD- and [Aliqua ][Cl]-imp egna ed algina e ae ogels (Zn-IL-ALG), Zn(II)-AHBD-imp egna ed algina e ae ogels (Zn-ALG), blank algina e ae ogels (ALG) and pu e Zn(II)-AHBD ca alys (Zn), espec i ely. 2.4. Ae ogels Images The images o he imp egna ed algina e and silica ae ogels a e p esen ed in he Figu es 8and 9, espec i ely. Figu e 8shows images o se e al algina e ae ogels, namely, blank ae ogel sample (a), Zn(II)-AHBD-imp egna ed ae ogel (b), Zn(II)-AHBD+[Aliqua ][Cl]- imp egna ed ae ogel (c) and ae ogel imp egna ed only wi h [Aliqua ][Cl] (d). Zn(II)-AHBD- imp egna ed ae ogels (Figu e 8b,c) p esen a b own colou , indica ing he p esence o he Zn(II)-AHBD ca alys in he ma ix. The same cha ac e is ics we e obse ed o he ex e io and in e io o he imp egna ed ae ogels, indica ing a homogeneous loading o he whole ae ogel monoli h. [Aliqua ][Cl]-imp egna ed samples (Figu e 8d) p esen ed a yellowish appea ance due o he p esence o he ionic liquid, which con as ed wi h he blank samples (Figu e 8a). Again, a homogeneous loading o he whole ae ogel monoli h was obse ed. Ca alys s 2021, 11, x FOR PEER REVIEW 8 o 17 imp egna ed ae ogels (Figu e 7, Zn-ALG) and i was possible o obse e ha he Zn(II)- AHBD cha ac e is ic peaks appea ed. This esul indica es ha al hough in low amoun s, he Zn(II)-AHBD complex was success ully imp egna ed in o he algina e ae ogels. Figu e 7. X- ay di ac ion pa e ns o Zn(II)-AHBD- and [Aliqua ][Cl]-imp egna ed algina e ae ogels (Zn-IL-ALG), Zn(II)-AHBD-imp egna ed algina e ae ogels (Zn-ALG), blank algina e ae ogels (ALG) and pu e Zn(II)-AHBD ca alys (Zn), espec i ely. 2.4. Ae ogels Images The images o he imp egna ed algina e and silica ae ogels a e p esen ed in he Figu es 8 and 9, espec i ely. Figu e 8 shows images o se e al algina e ae ogels, namely, blank ae ogel sample (a), Zn(II)-AHBD-imp egna ed ae ogel (b), Zn(II)- AHBD+[Aliqua ][Cl]-imp egna ed ae ogel (c) and ae ogel imp egna ed only wi h [Aliqua ][Cl] (d). Zn(II)-AHBD-imp egna ed ae ogels (Figu e 8b,c) p esen a b own colou , indica ing he p esence o he Zn(II)-AHBD ca alys in he ma ix. The same cha ac e is ics we e obse ed o he ex e io and in e io o he imp egna ed ae ogels, indica ing a homogeneous loading o he whole ae ogel monoli h. [Aliqua ][Cl]- imp egna ed samples (Figu e 8d) p esen ed a yellowish appea ance due o he p esence o he ionic liquid, which con as ed wi h he blank samples (Figu e 8a). Again, a homogeneous loading o he whole ae ogel monoli h was obse ed. (a) (b) (c) (d) Figu e 8. Images o algina e ae ogels: algina e ae ogels, (a) blank, (b) Zn(II)-AHBD-imp egna ed, (c) Zn(II)-AHBD + [Aliqua ][Cl]-imp egna ed, (d) [Aliqua ][Cl]-imp egna ed. In Figu e 9a,b a e p esen ed images o he silica ae ogels SIL1 and SIL2. The i s sample is a blank ae ogel, ollowed by a Zn(II)-AHBD imp egna ed ae ogel and in he case o image 11b) also Zn(II)-AHBD+[Aliqua ][Cl] imp egna ed silica ae ogel. 5 10152025303540455055606570 2θ (º) Zn-IL-ALG Zn-ALG ALG Zn Figu e 8. Images o algina e ae ogels: algina e ae ogels, ( a ) blank, ( b ) Zn(II)-AHBD-imp egna ed, (c) Zn(II)-AHBD + [Aliqua ][Cl]-imp egna ed, (d) [Aliqua ][Cl]-imp egna ed. In Figu e 9a,b a e p esen ed images o he silica ae ogels SIL1 and SIL2. The i s sample is a blank ae ogel, ollowed by a Zn(II)-AHBD imp egna ed ae ogel and in he case o image 11b) also Zn(II)-AHBD+[Aliqua ][Cl] imp egna ed silica ae ogel. Ca alys s 2021,11, 872 8 o 16 Ca alys s 2021, 11, x FOR PEER REVIEW 8 o 16 Figu e 9. Images o Silica ae ogels: (a) SIL1: Blank and Zn(II)-AHBD imp egna ed, espec i ely; (b) SIL2: Blank, Zn(II)-AHBD imp egna ed and Zn(II)-AHBD + [Aliqua ][Cl] imp egna ed, espec- i ely. 2.5. Scanning Elec on Mic oscopy The SEM mic og aphs o silica and algina e ae ogels a e p esen ed in he Figu es 10 and 11, espec i ely. Two di e en magni ica ions we e pe o med, 5.000 and 30.000, o de ec di e en de ails o he su ace mo phology. Figu e 10. SEM images o silica ae ogels (SIL2): (a) blank sample, (b) Zn(II)-AHBD imp egna ion and (c) Zn(II)-AHBD + [Aliqua ][Cl] imp egna ion. The i s line co esponds o a 5.000 magni ica- ion and he second line 30.000 magni ica ion. No changes on he su ace mo phology o silica ae ogels a e he imp egna ion we e obse ed (Figu e 10). The e o e, he discussions on he e ec o imp egna ion on su ace mo phology will be ocused on he algina e ae ogels (Figu e 11). In Figu e 11a, we obse e ha he blank algina e ae ogel p esen s a high po ous open s uc u e, ypical o he su ace mo phology o algina e ae ogels [48]. On he o he hand, he Zn(II)-AHBD-imp egna ed algina e ae ogels (Figu e 11b ex- hibi linkages o g anula ma e ial, indica ing he deposi ion o Zn(II)-AHBD on he su - ace s uc u e o algina e ae ogel. When algina e ae ogels we e imp egna ed wi h Zn(II)- AHBD and [Aliqua ][Cl] (Figu e 11c), he algina e ma ix p esen ed no po es and in- c eased hickness. This sugges s a high abso p ion o [Aliqua ][Cl] and Zn(II)-AHBD om he e hanol medium and as consequence he change o he ex u al s uc u e o he ae o- gels. The same esul was ob ained when only [Aliqua ][Cl] was imp egna ed (Figu e 11d). The SEM images p esen ed a e ela ed o he sample imp egna ed du ing 48 h wi h 20 mL [Aliqua ][Cl] and 10 mL o e hanol, bu simila esul s we e ob ained o he o he s. Figu e 9. Images o Silica ae ogels: ( a ) SIL1: Blank and Zn(II)-AHBD imp egna ed, espec i ely; (b) SIL2 : Blank, Zn(II)-AHBD imp egna ed and Zn(II)-AHBD + [Aliqua ][Cl] imp egna ed, espec- i ely. 2.5. Scanning Elec on Mic oscopy The SEM mic og aphs o silica and algina e ae ogels a e p esen ed in he Figu es 10 and 11 , espec i ely. Two di e en magni ica ions we e pe o med, 5.000 and 30.000, o de ec di e en de ails o he su ace mo phology. Ca alys s 2021, 11, x FOR PEER REVIEW 8 o 16 Figu e 9. Images o Silica ae ogels: (a) SIL1: Blank and Zn(II)-AHBD imp egna ed, espec i ely; (b) SIL2: Blank, Zn(II)-AHBD imp egna ed and Zn(II)-AHBD + [Aliqua ][Cl] imp egna ed, espec- i ely. 2.5. Scanning Elec on Mic oscopy The SEM mic og aphs o silica and algina e ae ogels a e p esen ed in he Figu es 10 and 11, espec i ely. Two di e en magni ica ions we e pe o med, 5.000 and 30.000, o de ec di e en de ails o he su ace mo phology. Figu e 10. SEM images o silica ae ogels (SIL2): (a) blank sample, (b) Zn(II)-AHBD imp egna ion and (c) Zn(II)-AHBD + [Aliqua ][Cl] imp egna ion. The i s line co esponds o a 5.000 magni ica- ion and he second line 30.000 magni ica ion. No changes on he su ace mo phology o silica ae ogels a e he imp egna ion we e obse ed (Figu e 10). The e o e, he discussions on he e ec o imp egna ion on su ace mo phology will be ocused on he algina e ae ogels (Figu e 11). In Figu e 11a, we obse e ha he blank algina e ae ogel p esen s a high po ous open s uc u e, ypical o he su ace mo phology o algina e ae ogels [48]. On he o he hand, he Zn(II)-AHBD-imp egna ed algina e ae ogels (Figu e 11b ex- hibi linkages o g anula ma e ial, indica ing he deposi ion o Zn(II)-AHBD on he su - ace s uc u e o algina e ae ogel. When algina e ae ogels we e imp egna ed wi h Zn(II)- AHBD and [Aliqua ][Cl] (Figu e 11c), he algina e ma ix p esen ed no po es and in- c eased hickness. This sugges s a high abso p ion o [Aliqua ][Cl] and Zn(II)-AHBD om he e hanol medium and as consequence he change o he ex u al s uc u e o he ae o- gels. The same esul was ob ained when only [Aliqua ][Cl] was imp egna ed (Figu e 11d). The SEM images p esen ed a e ela ed o he sample imp egna ed du ing 48 h wi h 20 mL [Aliqua ][Cl] and 10 mL o e hanol, bu simila esul s we e ob ained o he o he s. Figu e 10. SEM images o silica ae ogels (SIL2): ( a ) blank sample, ( b ) Zn(II)-AHBD imp egna ion and ( c ) Zn(II)-AHBD + [Aliqua ][Cl] imp egna ion. The i s line co esponds o a 5.000 magni ica ion and he second line 30.000 magni ica ion. No changes on he su ace mo phology o silica ae ogels a e he imp egna ion we e obse ed (Figu e 10). The e o e, he discussions on he e ec o imp egna ion on su ace mo phology will be ocused on he algina e ae ogels (Figu e 11). In Figu e 11a, we obse e ha he blank algina e ae ogel p esen s a high po ous open s uc u e, ypical o he su ace mo phology o algina e ae ogels [48]. On he o he hand, he Zn(II)-AHBD-imp egna ed algina e ae ogels (Figu e 11b exhibi linkages o g anula ma e ial, indica ing he deposi ion o Zn(II)-AHBD on he su ace s uc u e o algina e ae ogel. When algina e ae ogels we e imp egna ed wi h Zn(II)- AHBD and [Aliqua ][Cl] (Figu e 11c), he algina e ma ix p esen ed no po es and inc eased hickness. This sugges s a high abso p ion o [Aliqua ][Cl] and Zn(II)-AHBD om he e hanol medium and as consequence he change o he ex u al s uc u e o he ae ogels. The same esul was ob ained when only [Aliqua ][Cl] was imp egna ed (Figu e 11d). The SEM images p esen ed a e ela ed o he sample imp egna ed du ing 48 h wi h 20 mL [Aliqua ][Cl] and 10 mL o e hanol, bu simila esul s we e ob ained o he o he s. Ca alys s 2021,11, 872 9 o 16 Ca alys s 2021, 11, x FOR PEER REVIEW 9 o 16 356 357 358 359 360 361 362 363 364 365 366 367 368 369 370 Figu e 11. SEM images o algina e ae ogels: (a) blank, (b) Zn(II)-AHBD imp egna ion, (c) 371 Zn(II)-AHBD + [Aliqua ][Cl] imp egna ion and (d) [Aliqua ][Cl] imp egna ion. The i s line co e-372 sponds o a 5.000 magni ica ion and he second line o a 30.000 magni ica ion. 373 374 2.6. A omic abso p ion s udies 375 The me al loading was de e mined by a omic abso p ion. All he samples we e ana- 376 lysed (excep he ones imp egna ed only wi h [Aliqua ][Cl]). Howe e , he only sample 377 o which Zn(II)-AHBD was de ec ed was he algina e ae ogel imp egna ed wi h Zn(II)- 378 AHBD (Zn-ALG). Fo all he o he samples i was no possible o quan i y he Zn(II)- 379 AHBD loading since i was below he de ec ion limi . The concen a ion ob ained o Zn- 380 ALG was only 1.99% (w/w). Fo Zn-IL-ALG, he p esence o Aliqua Cl has signi ican ly 381 educed he complex solubili y in he solu ion, dec easing he zinc concen a ion on he 382 ma e ials o bellow he de ec ion limi (which is 8 ppb). 383 384 Fo silica ae ogels, ex u al p ope ies seem o e idence a signi ican imp egna ion 385 le el, which was no de ec ed by he a omic abso p ion s udies, namely o Zn-SIL2. In 386 his case, he complex should ha e su e ed a p ocess o decomposi ion in con ac wi h 387 he silica ma e ial. The e o e bo h, ex u al esul s and he b own colo obse ed, a e no 388 due o he p esence o zinc, bu due o he p esence o he ligand AHBD. 389 390 391 2.7. Reac ions using imp egna ed ae ogels as ca alys s 392 Imp egna ed algina e and silica ae ogels we e e alua ed as ca aly ic sys ems o he 393 coupling eac ion be ween CO 2 and limonene oxide (Figu e 12). The esul s a e summa- 394 ized in Table 3. 395 396 397 398 399 400 401 402 403 Figu e 12. Syn hesis o cyclic ca bona es om CO2 and epoxides. 404 405 Based on ou p e ious s udies, all he eac ions we e pe o med o 48 hou s, a 353.2 406 K and 4 MPa, using 1 mL o limonene oxide [12,39,48,55]. I should be no ed ha he ae - 407 ogel was ne e used in di ec con ac wi h he liquid phase. All eac ions we e ca ied ou 408 main aining he ae ogel suppo ed in a me allic g id a he op o he eac o in con ac 409 d ) c ) b ) a ) Figu e 11. SEM images o algina e ae ogels: ( a ) blank, ( b ) Zn(II)-AHBD imp egna ion, ( c ) Zn(II)-AHBD + [Aliqua ][Cl] imp egna ion and ( d ) [Aliqua ][Cl] imp egna ion. The i s line co esponds o a 5.000 magni ica ion and he second line o a 30.000 magni ica ion. 2.6. A omic Abso p ion S udies The me al loading was de e mined by a omic abso p ion. All he samples we e analysed (excep he ones imp egna ed only wi h [Aliqua ][Cl]). Howe e , he only sample o which Zn(II)-AHBD was de ec ed was he algina e ae ogel imp egna ed wi h Zn(II)- AHBD (Zn-ALG). Fo all he o he samples, i was no possible o quan i y he Zn(II)-AHBD loading since i was below he de ec ion limi . The concen a ion ob ained o Zn-ALG was only 1.99% (w/w). Fo Zn-IL-ALG, he p esence o Aliqua Cl has signi ican ly educed he complex solubili y in he solu ion, dec easing he zinc concen a ion on he ma e ials o bellow he de ec ion limi (which is 8 ppb). Fo silica ae ogels, ex u al p ope ies seem o e idence a signi ican imp egna ion le el, which was no de ec ed by he a omic abso p ion s udies, namely o Zn-SIL2. In his case, he complex should ha e su e ed a p ocess o decomposi ion in con ac wi h he silica ma e ial. The e o e, bo h ex u al esul s and he b own colo obse ed a e no due o he p esence o zinc, bu due o he p esence o he ligand AHBD. 2.7. Reac ions Using Imp egna ed Ae ogels as Ca alys s Imp egna ed algina e and silica ae ogels we e e alua ed as ca aly ic sys ems o he coupling eac ion be ween CO 2 and limonene oxide (Figu e 12). The esul s a e summa ized in Table 3. Ca alys s 2021, 11, x FOR PEER REVIEW 9 o 16 Figu e 11. SEM images o algina e ae ogels: (a) blank, (b) Zn(II)-AHBD imp egna ion, (c) Zn(II)-AHBD + [Aliqua ][Cl] imp egna ion and (d) [Aliqua ][Cl] imp egna ion. The i s line co esponds o a 5.000 magni ica ion and he second line o a 30.000 magni ica ion. 2.6. A omic Abso p ion S udies The me al loading was de e mined by a omic abso p ion. All he samples we e ana- lysed (excep he ones imp egna ed only wi h [Aliqua ][Cl]). Howe e , he only sample o which Zn(II)-AHBD was de ec ed was he algina e ae ogel imp egna ed wi h Zn(II)- AHBD (Zn-ALG). Fo all he o he samples, i was no possible o quan i y he Zn(II)- AHBD loading since i was below he de ec ion limi . The concen a ion ob ained o Zn- ALG was only 1.99% (w/w). Fo Zn-IL-ALG, he p esence o Aliqua Cl has signi ican ly educed he complex solubili y in he solu ion, dec easing he zinc concen a ion on he ma e ials o bellow he de ec ion limi (which is 8 ppb). Fo silica ae ogels, ex u al p ope ies seem o e idence a signi ican imp egna ion le el, which was no de ec ed by he a omic abso p ion s udies, namely o Zn-SIL2. In his case, he complex should ha e su e ed a p ocess o decomposi ion in con ac wi h he silica ma e ial. The e o e, bo h ex u al esul s and he b own colo obse ed a e no due o he p esence o zinc, bu due o he p esence o he ligand AHBD. 2.7. Reac ions Using Imp egna ed Ae ogels as Ca alys s Imp egna ed algina e and silica ae ogels we e e alua ed as ca aly ic sys ems o he coupling eac ion be ween CO2 and limonene oxide (Figu e 12). The esul s a e summa- ized in Table 3. Figu e 12. Syn hesis o cyclic ca bona es om CO2 and epoxides. Based on ou p e ious s udies, all he eac ions we e pe o med o 48 h, a 353.2 K and 4 MPa, using 1 mL o limonene oxide [39,53,54]. I should be no ed ha he ae ogel was ne e used in di ec con ac wi h he liquid phase. All eac ions we e ca ied ou Figu e 12. Syn hesis o cyclic ca bona es om CO2and epoxides. 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