doctoral dissertation
Matevž Roškarič (Author), Gregor Žerjav (Mentor)

Abstract

Grafitni ogljikov nitrid (g-C3N4) predstavlja obetavnega kandidata za remediacijo okolja, vendar določene neželene lastnosti omejujejo njegovo fotokatalitsko aktivnost (npr. nizka specifična površina in visoka tendenca za rekombinacijo nosilcev naboja). Le-te lahko izboljšamo z uporabo klasičnega optimizacijskega postopka (tj. korak za korakom), ki pa tipično ne daje optimalnih rezultatov. Kot alternativo lahko uporabimo številne statistične metode, kot je npr. optimizacijski postopek Simplex, s katerim smo izboljšali ne le specifično površino g-C3N4 (zastavljena cenilna funkcija), ampak tudi druge morfološke in opto-elektronske lastnosti. V le nekaj korakih smo pridobili znatno izboljšan fotokatalizator, ki je v celoti razgradil modelno onesnažilo bisfenol A (BPA) pri uporabi vidne svetlobe. Fotokatalizator g-C3N4 smo tudi optimizirali po njegovi sintezi s pomočjo aktivacije pri povišani temperaturi v CO2 atmosferi. Ponovno nismo izboljšali le specifične površine, ampak tudi druge opto-elektronske in strukturne lastnosti, katere so omogočile skoraj popolno razgradnjo BPA z uporabo simulirane sončne svetlobe. V obeh primerih (Simplex ali CO2 aktivacija) smo deformirali strukturo idealnega 2D g-C3N4 fotokatalizatorja in vnesli defekte, kar je izboljšalo ne le opto-elektronskih lastnosti, ampak omogočilo tudi nastanek singletnega kisika. Le-ta je omogočil povečano razgradnjo BPA in tudi njegovih analogov (BPF, BPS in BPAF), kakor tudi selektivno razgradnjo izbranih farmacevtskih učinkovin (paracetomol, acetilsalicilna kislina, salicilna kislina, benzojska kislina in kofein). Kljub visoki stabilnosti v vodnih medijih čisti g-C3N4 materiali izkazujejo manjšo deaktivacijo pri ponovni uporabi. Da izboljšamo stabilnost in druge negativne lastnosti čistih g-C3N4 (CN) materialov, jih lahko združimo s TiO2 v hibridne materiale. Ugotovili smo, da je optimalno masno razmerje med obema komponentama 1:1 in da podaljšana sinteza hibridnih materialov v zraku (24 ur) izboljša stik do optimalne mere, kar poveča fotokatalitsko aktivnost. Ta pojav je opazen ne glede na izbrano morfologijo TiO2 (nanosfere TP ali heksagonalni delci TH) komponente (CNTP-24 ali CNTH 24 fotokatalizatorja). Morfologija TiO2 pa ima lahko tudi druge pozitivne lastnosti, saj lahko nastale kisikove praznine in Ti3+ v TiO2 vplivajo na opto-elektronske lastnosti kompozita. Zato je TiO2 v obliki nanopalčk (TR) doprinesel največje izboljšanje, kadar je združen v hibridni material (CNTR-2) z g-C3N4 (CN), v primerjavi s komercialnimi TP. Hkrati, če te kompozite dodatno tretiramo v prisotnosti N2 pri povišani temperaturi, dosežemo preoblikovanje g-C3N4 in znatno izboljšamo opto-elektronske lastnosti hibridnih materialov. Zato le-ti izkazujejo do 300 % povečano fotokatalitsko aktivnost razgradnje BPA pri uporabi vidne svetlobe v primerjavi z neobdelanim hibridnim materialom. Dodatno lahko povečamo fotokatalitsko aktivnost z nanosom plazmonske kovine platine (Pt), kjer preferenčna lokacija nanosa Pt nanodelcev vpliva na aktivnost kompozitov zaradi različnih interakcij Pt z nosilcem (g-C3N4 ali TiO2). Ker so vsi postopki spreminjanja morfologije TiO2 potratni (čas, denar, kemikalije), smo z uporabo hitre in zelene mehano-kemijske sinteze tvorili hibridne g-C3N4/TiO2 materiale. Le-ti so izkazovali podobno izboljšane fotokatalitske odzive kot npr. CNTR-2 fotokatalizator, kar jih naredi obetavne za realne aplikacije. Tako je potrebno upoštevati celo vrsto parametrov in možnosti, kadar želimo tvoriti napredne hibridne fotokatalizatorje za remediacijo okolja.

Keywords

grafitni ogljikov nitrid (g-C3N4);hibridni materiali;razvoj fotokatalizatorjev;heterogena fotokataliza;okoljska remediacija;doktorske disertacije;

Data

Language: Slovenian
Year of publishing:
Typology: 2.08 - Doctoral Dissertation
Organization: UM FKKT - Faculty of Chemistry and Chemical Engineering
Publisher: [M. Roškarič]
UDC: 544.162:544.526.5(043.3)
COBISS: 217790979 Link will open in a new window
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Other data

Secondary language: English
Secondary title: Development of advanced graphitic carbon nitride based catalysts for environmental applications
Secondary abstract: Graphitic carbon nitride (g-C3N4) is a promising candidate for environmental remediation, but certain undesirable properties limit its photocatalytic activity (e.g. a low specific surface area and a high tendency for carrier recombination). They can be improved by a classical optimisation process (i.e. step by step), although this method usually does not lead to optimal results. As an alternative, different statistical methods can be used, such as Simplex method, which not only improved the specific surface area of g-C3N4 (fitness function), but also enhanced other morphological and opto-electronic properties. In just a few steps, we obtained a significantly improved photocatalyst that completely degraded the model pollutant bisphenol A (BPA) under visible light. g-C3N4 was further optimised by activating it at an elevated temperature in a CO2 atmosphere. Here, not only the specific surface area was improved, but also the opto-electronic and structural properties that enabled almost complete degradation of BPA under simulated sunlight. In both cases (Simplex or CO2 activation), the structure of the ideal 2D g-C3N4 photocatalyst was deformed and defects were introduced that not only improved the opto-electronic properties but also enabled the generation of singlet oxygen. This increased the degradation of BPA and its analogues (BPF, BPS and BPAF) as well enabled the selective degradation of pharmaceutical compounds (paracetamol, acetylsalicylic acid, salicylic acid, benzoic acid and caffeine). Despite the high stability of the pure g-C3N4 materials in aqueous media, they exhibit a certain degree of deactivation. To improve the stability and overcome other negative properties of the pure g-C3N4 (CN) materials, they can be combined with TiO2 to form hybrid materials. We found that the optimal mass ratio between the two components is 1:1 and that a longer synthesis of the hybrid materials in air (24 hours) improves the contact to an optimal level, which increases the photocatalytic activity. This effect is observed regardless of the chosen morphology of the TiO2 component (whether TP nanospheres or TH hexagonal particles) in the CNTP-24 or CNTH-24 photocatalysts. However, the morphology of TiO2 can have further positive effects, as the resulting oxygen vacancies and Ti3+ in TiO2 can influence the opto-electronic properties of the composites. For example, TiO2 in the form of nanorods (TR) in combination with g-C3N4 (CN) in a hybrid material (CNTR-2) offered the greatest improvement compared to commercial TP. When these composites are further treated in the presence of N2 at elevated temperatures, the g-C3N4 is transformed, which significantly improves the opto-electronic properties of the hybrid materials. As a result, these materials show up to 300% increased photocatalytic activity in the degradation of BPA under visible light compared to untreated hybrid material. The photocatalytic activity can be further enhanced by the deposition of the plasmonic metal platinum (Pt), whereby the preferred site of deposition of Pt nanoparticles influences the activity of the composites due to the different interactions of Pt with the support (g-C3N4 or TiO2). Since all methods to modify the morphology of TiO2 are resource intensive (time, money, chemicals), we used a fast and environmentally friendly mechano-chemical synthesis to prepare hybrid g-C3N4/TiO2 materials. These materials showed similarly improved photocatalytic responses as the CNTR-2 photocatalyst, which makes them promising for real applications. Therefore, a wide range of parameters and possibilities must be considered when developing advanced hybrid photocatalysts for environmental remediation.
Secondary keywords: graphitic carbon nitride (g-C3N4);hybrid materials;development of photocatalysts;heterogeneous photocatalysis;environmental remediation;
Type (COBISS): Doctoral dissertation
Thesis comment: Univ. v Mariboru, Fak. za kemijo in kemijsko tehnologijo
Pages: XXIII, 256 str.
ID: 24184555