Influence of different carbon monolith preparation parameters on pesticide adsorption

The capacity of carbon monolith for pesticide removal from water, and the mechanism of pesticide interaction with carbon surface were examined. Different carbon monolith samples were obtained by varying the carbonization and activation parameters. In order to examine the role of surface oxygen groups in pesticide adsorption, carbon monolith surface was functionalized by chemical treatment in HNO3, H2O2 and KOH. The surface properties of the obtained samples were investigated by BET surface area, pore size distribution and temperature-programmed desorption. Adsorption of pesticides from aqueous solution onto activated carbon monolith samples was studied by using five pesticides belonging to different chemical groups (acetamiprid, dimethoate, nicosulfuron, carbofuran and atrazine). Presented results show that higher temperature of carbonization and the amount of activating agent allow obtaining microporous carbon monolith with higher amount of surface functional groups. Adsorption properties of the activated carbon monolith were more readily affected by the amount of the surface functional groups than by specific surface area. Results obtained by carbon monolith functionalisation showed that π-π interactions were the main force for adsorption of pesticides with aromatic structure, while acidic groups play an important role in adsorption of pesticides with no aromatic ring in the chemical structure

Mikrokapilarni reaktor za konverziju CO u CO2

The alcrocapillary carbon supporting carposite platinum catalyst rOd distributed. Palls pores has been Installed into inside chefurnace and tested as oxidation of reactor F6=carbon sonoxide catalytic inlet of the rod was connected carboa sloxide. The valve and outlet was connected-o a tuse supplyinz co-o2 the to she ras. Las chromatogrash tases reselting E=o= chein orde detect product COg has been detested cacalycie Feaocion. The 200-556 0. in with 95% yield the temperature range

Korelacija stepena konverzije i količine oslobođenih supstanci iz dentalnih kompozitnih cemenata

This study examined the possible correlation between the degree of conversion (DC) and the amount of substances eluted from three commercial cured resin-based cements. The DC of the various resin-based cements was measured by Raman spectroscopy, while the quantity of unreacted monomers released from the cement matrix (triethylene glycol dimethacrylate, TEGDMA, urethane dimethacrylate, UDMA, 2-hydroxyethyl methacrylate, HEMA and bisphenol A) was determined by high pressure liquid chromatography (HPLC). The obtained results, after multiple statistical evaluation (one way ANOVA, LSD post hoc test), showed no significant differences in the DC values between the resin cements. On the contrary, the results of the HPLC analysis depicted statistically significant differences between the three materials with respect to the amount of leached monomers. In addition, no correlation between the DC and the amount of eluted substances from the tested cured composite cements was found.Rad istražuje moguću korelaciju stepena konverzije (DC) i količine oslobođenih monomernih supstanci iz tri komercijalna preparata kompozitnih dentalnih cemenata. Stepen konverzije kompozitnih cemenata određen je metodom Raman spektroskopije, dok je količina neizreagovalih i oslobođenih monomera iz cementnog matriksa detektovana pomoću HPLC metode. Rezultati dobijeni nakon višestruke statističke evaluacije (one way ANOVA, LSD past hoc test) ne pokazuju značajne razlike u stepenu konverzije različitih preparata kompozitnih cemenata. Nasuprot tome, rezultati HPLC analize beleže značajne razlike u količini i vrsti monomernih supstanci otpuštenih iz kompozitnih cemenata. Takođe, statistička analiza u okviru ove studije nije pokazala korelaciju stepena konverzije ispitivanih kompozitnih dentalnih cemenata i količine oslobođenih supstanci iz ovih materijala

Thermal treatment influence on the surface characteristics of the borondoped hydrothermal carbon

Structural and surface characterization of pristine and boron doped carbonized hydrothermal carbons (CHTC) is reported. Boron was introduced into glucose precursor solution with concentration of 0.2% and 1%. Following hydrothermal treatment, samples were carbonized to 1000oC and examined by Raman spectroscopy and temperature programmed desorption. Characterization of obtained samples as material for carbon paste electrode was performed by cyclic voltammetry measurements of the Fe (CN)6 3-/4- redox couple. Structural analysis showed that lower boron content in precursor solution induced structure ordering, while higher amount of boron caused structural disorder of CHTC sample. Boron presence in CHTC samples reduced number of surface active sites for oxygen adsorption and consequently improved their electrochemical response as electrode material for carbon paste electrode

Mathematical modeling of pesticide adsorption on activated hemp fibers

Activated carbon obtained by carbonization and activation of waste hemp fibers was used as an efficient, low-cost sorbent for pesticide removal. Data obtained from batch and continuous process of pesticide adsorption was used for development of the mathematical model that describes the phenomenon of pesticide transport through the porous sorbent matrices. Effective diffusion coefficient and the pesticide concentration profile within the activated hemp fibers, obtained as results of proposed model, give the insight in the mechanism and the rate of adsorption process and pesticide transport through the sorbent. A good agreement between model prediction and the experimental data indicates that the proposed mathematical model can be successfully used for optimization and selection of appropriate adsorption process for pesticide removal

ESI-MS spectra of 3-cyano-4-(substituted phenyl)-6-phenyl-2(1H)-pyridinones

Twelve 3-cyano-4-(substituted phenyl)-6-phenyl-2(1H)-pyridinones were investigated by tandem mass spectrometry using positive as well as negative electrospray ionization. The influence of the electron affinity of the substituent and the steric effect on the fragmentation is discussed. Pyridinones with a substituent of low proton affinity show loss of water, HCN or benzene from the pyridinone ring in the first step of MS2 fragmentations. Oppositely, if a substituent with high proton affinity is present on the phenyl ring in the 4-position of pyridinone, the fragmentation paths are complex, depending mainly on the substituent proton acceptor ability. Elimination of neutral molecules CO, HCN, H2O, PhH (benzene) or Ph and CN radicals are fragmentation processes common for all compounds in the subsequent steps of the fragmentations

One-step hydrothermal synthesis of photocatalytically active TiO2/carbon composite

TiO2/carbon composite (TiO2/HTC), synthesized by hydrothermal carbonization, was characterized by thermogravimetric analysis, nitrogen adsorption–desorption isotherms and X-ray diffraction. The possibility of using TiO2/HTC as photocatalysts for UV and visible light assisted degradation of methylene blue inaqueous solution was examined. It was found that carbon presence in TiO2/HTC leads to the higher porosity and increase in the share of photocatalytically active anatase phase. Compared to the hydrothermally synthesized TiO2, TiO2/HTC showed the superior photocatalytic activity under UV irradiation. In addition, TiO2/HTC show high recycling ability with degradation ratio of methylene blue higher than 81% after five cycles. Also, TiO2/HTC is expected to be a promising candidate for photocatalytic processes using visible light.Physical chemistry 2016 : 13th international conference on fundamental and applied aspects of physical chemistry; Belgrade (Serbia); 26-30 September 2016

Određivanje odabranih steroida u uzorcima komunalne otpadne vode

Komunalne otpadne vode i efluenti iz postrojenja za prečišćavanje otpadnih voda predstavljaju značajan izvor zagađujućih materija u vodenoj sredini. Studije su pokazale da se steroidna jedinjenja u postrojenjima za tretman ne uklanjaju u potpunosti, kao i da prisustvo steroida u vodi, čak i pri veoma niskim koncentracijama, može izazvati brojne neželjene efekte. U ovom radu analizirani su kompozitni uzorci otpadne vode, uzeti tokom pet dana sa dva ispusta komunalne vode u Novom Sadu. U uzorcima otpadne vode ispitivano je prisustvo 20 najčešće detektovanih steroidnih hormona i sterola optimizovanom metodom tečne hromatografije visokih performansi u sprezi sa tandem masenom spektrometrijom. Pored rastvornog oblika steroida, analizirana je i frakcija adsorbovana na suspendovanoj materiji

Carbon cryogel as an adsorbent for removal of Cd(II), Zn(II) and Ni(II) ions from water

Zagađenje vodenih tokova teškim metalima je jedan od najakutnijih ekoloških problema današnjice. S obzirom na to da teški metali nisu biorazgradivi, oni se akumuliraju u životnoj sredini i na taj način ulaze u lanac ishrane ljudi i životinja, pa kao veoma toksične materije, mogu izazivati niz opasnih i često neizlečivih bolesti. Iz tog razloga, istraživači godinama u nazad razvijaju nove i usavršavaju postojeće tehnike za prečišćavanje otpadnih voda od ovih zagađujućih materija [1]. Za prečišćavanje vode zagađene teškim metalima mogu se koristiti različite metode: hemijska precipitacija, elektrohemijski tretmani, filtracija, reverzna osmoza, jonska izmena, membranski procesi, adsorpcija. Jedna od najčešće korišćenih je adsorpcija, koja zbog mogućnosti regenerisanja adsorbenta, odgovarajućim desorpcionim procesom, predstavlja veoma efektivnu i ekonomičnu metodu. Zahvaljujući razvijenoj specifičnoj površini i poroznosti, kao i prisustvu funkcionalnih grupa na površini, različiti ugljenični materijali pokazuju visoku efikasnost u uklanjanju teških metala iz vode. Karbon kriogel (CC) predstavlja ugljenični materijal razvijene mezoporoznosti čije se adsorpcione karakteristike mogu poboljšati optimizacijom i kontrolisanjem parametara dobijanja. U ovom radu je ispitana mogućnost uklanjanja jona teških metala (Cd2+, Ni2+ i Zn2+) iz vode, korišćenjem karbon kriogela i hemijski modifikovanog karbon kriogela. Prvi korak u sintezi karbon kriogela je polikondenzacija rezorcinola i formaldehida, u prisustvu natrijum-karbonata kao katalizatora. Organski kriogel pripremljen je solgel tehnologijom uz naknadno sušenje postupkom zamrzavanja, dok je karbonizacija organskog kriogela vršena u inertnoj atmosferi argona na temperaturi od 800 o C [2]. U cilju poboljšanja adsorpcionih karakteristika karbon kriogela, izvršeno je hemijsko modifikovanje korišćenjem 5 M HNO3 . Karakterizacija materijala izvršena je merenjem specifične površine BET metodom, određivanjem tačke nultog naelektrisanja metodom masene titracije, kao i određivanjem vrsta funkcionalnih grupa prisutnih na površini materijala, metodom infracrvene spektroskopije sa Furijeovom transformacijom (FTIR). Ispitan je uticaj pH vrednosti rastvora, početne koncentracije jona metala u rastvoru, kao i vremena kontakta na adsorpciju teških metala uzorcima karbon kriogela.Primenjenom hemijskom modifikacijom karbon kriogela ne dolazi do bitnijih promena u specifičnoj površini i poroznosti materijala. S druge strane, ovim postupkom dolazi do izmene površinske hemije materijala, uvođenjem novih, i povećanjem broja postojećih kiselih površinskih grupa, što je pokazano FTIR analizom i smanjenjem vrednosti tačke nultog naelektrisanja sa pHPZC = 9,3 na pHPZC = 3,1. Adsorpcija jona teških metala na modifikovanom i nemodifikovanom karbon kriogelu vršena je na pH = 6, jer pri ovoj pH vrednosti materijali pokazuju najveći adsorpcioni kapacitet, a ujedno je izborom ove pH izbegnuta precipitacija hidroksida metala. Izmene u hemiji površine dovode i do izmena adsorpcionih karakteristika karbon kriogela. Kako površinske grupe predstavljaju aktivna mesta za adsorpciju jona teških metala, povećanje količine površinskih grupa kod modifikovanog karbon kriogela dovodi do višestrukog povećanja adsorpcionog kapaciteta

Characterisation of surface oxygen groups on different carbon materials by the Boehm method and temperature-programmed desorption

The surface characteristics of different carbon materials: activated carbon, carbon felt, glassy carbon and a porous carbon monolith were investigated. The specific surface area was examined by the BET method with N(2) adsorption, the amount and the type of surface oxygen groups by Boehm titration as well as by temperature-programmed desorption (TPD). By comparing the results obtained using BET analysis with those of TPD and the Boehm method, it was found that the number of surface groups was not proportional to the specific surface area. The total amount of oxygen groups, obtained by TPD, is higher than the amount obtained by Boehms method for porous samples. The inconsistencies between these results originate from the fact that the Boehm method is limited to the determination of acidic and basic groups, whereas TPD provides information on the total number of all surface oxygen groups. In addition, the presence of porosity could reduce the solvent-accessible surface in the Boehm method. The TPD profiles of CO evolution showed the presence of a low temperature maximum, below 650 K, which originates from CO(2) reduction on the carbon material surface