94 research outputs found
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 Ļ-Ļ 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 koliÄine osloboÄenih 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 moguÄu korelaciju stepena konverzije (DC) i koliÄine osloboÄenih monomernih supstanci iz tri komercijalna preparata kompozitnih dentalnih cemenata. Stepen konverzije kompozitnih cemenata odreÄen je metodom Raman spektroskopije, dok je koliÄina neizreagovalih i osloboÄenih monomera iz cementnog matriksa detektovana pomoÄu HPLC metode. Rezultati dobijeni nakon viÅ”estruke statistiÄke evaluacije (one way ANOVA, LSD past hoc test) ne pokazuju znaÄajne razlike u stepenu konverzije razliÄitih preparata kompozitnih cemenata. Nasuprot tome, rezultati HPLC analize beleže znaÄajne razlike u koliÄini i vrsti monomernih supstanci otpuÅ”tenih iz kompozitnih cemenata. TakoÄe, statistiÄka analiza u okviru ove studije nije pokazala korelaciju stepena konverzije ispitivanih kompozitnih dentalnih cemenata i koliÄine osloboÄenih 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 adsorptionādesorption 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
OdreÄivanje odabranih steroida u uzorcima komunalne otpadne vode
Komunalne otpadne vode i efluenti iz postrojenja za preÄiÅ”Äavanje otpadnih voda predstavljaju znaÄajan izvor zagaÄujuÄih 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, Äak 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 najÄeÅ”Äe detektovanih steroidnih hormona i sterola optimizovanom metodom teÄne 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
ZagaÄenje vodenih tokova teÅ”kim metalima je jedan od najakutnijih ekoloÅ”kih
problema danaŔnjice. S obzirom na to da teŔki metali nisu biorazgradivi, oni se akumuliraju
u životnoj sredini i na taj naÄin ulaze u lanac ishrane ljudi i životinja, pa kao veoma toksiÄne
materije, mogu izazivati niz opasnih i Äesto neizleÄivih bolesti. Iz tog razloga, istraživaÄi
godinama u nazad razvijaju nove i usavrÅ”avaju postojeÄe tehnike za preÄiÅ”Äavanje otpadnih
voda od ovih zagaÄujuÄih materija [1]. Za preÄiÅ”Äavanje vode zagaÄene teÅ”kim metalima
mogu se koristiti razliÄite metode: hemijska precipitacija, elektrohemijski tretmani, filtracija,
reverzna osmoza, jonska izmena, membranski procesi, adsorpcija. Jedna od najÄeÅ”Äe
koriÅ”Äenih je adsorpcija, koja zbog moguÄnosti regenerisanja adsorbenta, odgovarajuÄim
desorpcionim procesom, predstavlja veoma efektivnu i ekonomiÄnu metodu. ZahvaljujuÄi
razvijenoj specifiÄnoj povrÅ”ini i poroznosti, kao i prisustvu funkcionalnih grupa na povrÅ”ini,
razliÄiti ugljeniÄni materijali pokazuju visoku efikasnost u uklanjanju teÅ”kih metala iz
vode. Karbon kriogel (CC) predstavlja ugljeniÄni materijal razvijene mezoporoznosti Äije
se adsorpcione karakteristike mogu poboljŔati optimizacijom i kontrolisanjem parametara
dobijanja. U ovom radu je ispitana moguÄnost uklanjanja jona teÅ”kih metala (Cd2+, Ni2+ i
Zn2+) iz vode, koriÅ”Äenjem 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 suŔenje postupkom zamrzavanja, dok je karbonizacija
organskog kriogela vrŔena u inertnoj atmosferi argona na temperaturi od 800 o
C [2]. U
cilju poboljŔanja adsorpcionih karakteristika karbon kriogela, izvrŔeno je hemijsko
modifikovanje koriÅ”Äenjem 5 M HNO3
. Karakterizacija materijala izvrŔena je merenjem
specifiÄne povrÅ”ine BET metodom, odreÄivanjem taÄke nultog naelektrisanja metodom
masene titracije, kao i odreÄivanjem vrsta funkcionalnih grupa prisutnih na povrÅ”ini
materijala, metodom infracrvene spektroskopije sa Furijeovom transformacijom (FTIR).
Ispitan je uticaj pH vrednosti rastvora, poÄetne koncentracije jona metala u rastvoru, kao i
vremena kontakta na adsorpciju teŔkih metala uzorcima karbon kriogela.Primenjenom hemijskom modifikacijom karbon kriogela ne dolazi do bitnijih
promena u specifiÄnoj povrÅ”ini i poroznosti materijala. S druge strane, ovim postupkom
dolazi do izmene povrÅ”inske hemije materijala, uvoÄenjem novih, i poveÄanjem broja
postojeÄih kiselih povrÅ”inskih grupa, Å”to je pokazano FTIR analizom i smanjenjem
vrednosti taÄke nultog naelektrisanja sa pHPZC = 9,3 na pHPZC = 3,1. Adsorpcija jona teÅ”kih
metala na modifikovanom i nemodifikovanom karbon kriogelu vrŔena je na pH = 6, jer pri
ovoj pH vrednosti materijali pokazuju najveÄi adsorpcioni kapacitet, a ujedno je izborom
ove pH izbegnuta precipitacija hidroksida metala. Izmene u hemiji povrŔine dovode i do
izmena adsorpcionih karakteristika karbon kriogela. Kako povrŔinske grupe predstavljaju
aktivna mesta za adsorpciju jona teÅ”kih metala, poveÄanje koliÄine povrÅ”inskih grupa kod
modifikovanog karbon kriogela dovodi do viÅ”estrukog poveÄanja 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
- ā¦