Facultatea de Chimie şi Tehnologie Chimică / Faculty of Chemistry and Chemical Technology

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Author: search.filters.author.Duca, GheorgheEnd date: 2022

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    Participarea substanțelor tiolice în procese de autopurificare chimică a apelor naturale: Monografie
    (CEP USM, 2022) Blonschi, Vladislav; Gladchi, Viorica; Duca, Gheorghe
    Prezenta lucrare este consacrată evaluării aportului substanțelor tiolice în procesele de autopurificare chimică a sistemelor acvatice, prin stabilirea unor legități de transformare fotochimică ale acestora.
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    Production, structure and photocatalytic properties of nanotubular TiO2 [Articol]
    (2020) Duca, Gheorghe; Covaliov, Victor; Covaliova, Olga
    Photocatalytic processes are among the most efficient treatment methods of waters polluted with recalcitrant organic substances. Nanotubular TiO2 arrays with photocatalytic properties were obtained in the process of titanium anodic oxidation in the fluoridecontaining electrolyte. Under the proposed conditions of electrolysis, a coherent system of tightly adjoining nanotubes was formed with the internal diameter of 60-80 nm and walls thickness up to 60-65 nm, the tubes height being dependent on process duration, reaching over 200 mkm. It was shown that it is the specifics of the formation, destruction and renewal of the barrier layer that determines the tubular structure of anodic titanium coatings formed. Various anodizing regimes were proposed to obtain the different TiO2-containing structures-nanotubular and fine dispersed ones. Subsequent annealing of nanotubular titanium dioxide provokes the series of structural-phase transformations, modifying its photocatalytic properties. The nanotubular systems thus obtained were tested as photo-catalysts, both as compact coatings and as fine dispersed particles, in the especially developed integrated photoreactor. It was shown that using the proposed equipment and photocatalysts produced, the efficient photodestruction of the persistent organic pollutants such as benozhiazol (BT) can be reached due to the combination of chemical and physical effects.
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    Intensificarea fitochimică a emisiei biohidrogenului în procesele de fermentare anaerobă a biomasei [Articol]
    (2013) Covaliov, Victor; Duca, Gheorghe; Bobeică, Valentin; Covaliova, Olga
    Se examinează problemele producerii şi utilizării hidrogenului ca agent energetic ecologic. Se analizează, în special, realizările înregistrate în ceea ce priveşte intensifi carea şi reducerea consumurilor materiale şi energetice pentru obţinerea biohidrogenului în procesul purificării deşeurilor agroindustriale lichide prin metoda fermentării anaerobe, utilizându-se procedeul original de redirecţionare cu ajutorul unor microstimulenţi fi tochimici a metanogenezei în vederea formării hidrogenului, optimizării funcţionale şi energetice a bioreactorului şi utilizării unor procedee ecologo-economice de purifi care a biohidrogenului.
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    Removal of Direct Dyes from Textile Wastewater by Means of Combined Methods [Articol]
    (2009) Matveevici, Vera; Duca, Gheorghe; Gonța, Maria; Iambarțev, Viorica; Mocanu, Lilia
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    Îndepărtarea cefalexinei din soluții apoase utilizând procesul fotocatalitic fenton [Articol]
    (2021) Mocanu, Larisa; Gonța, Maria; Matveevici, Vera; Duca, Gheorghe; Porubin-Schimbător, Veronica
    În această lucrare s-a studiat procesul de degradare și oxidare/mineralizare a cefalexinei (CLX) din sisteme model prin procese de oxidare avansată cu utilizarea reagentului Fenton la iradiere cu raze UV (λ=254 nm). S-au determinat condițiile optime de oxidare fotocatalitică a CLX în funcție de diferiți parametri fizico-chimici: pH-ul mediului de reacție, timpul de reacție, concentrația oxidantului (H2O2), a catalizatorului (ioni Fe(II)) și a substratului. După cum s-a stabilit, creșterea concentrației de H2O2 față de cea optimă inhibă formarea radicalilor hidroxil și duce la generarea radicalilor HO2 •, care au un potențial de oxidare mai mic comparativ cu •OH. Iar pe măsură ce concentrația catalizatorului crește față de cea optimă, excesul de ioni Fe(II) reacționează cu radicalul hidroxil și, prin urmare, se reduce eficiența procesului. În baza rezultatelor obținute la foto-oxidarea catalitică a sistemului ce conține 50 mg/L CLX în prezența a 3,4 mg/L peroxid de hidrogen și 5,6 mg/L ioni Fe(II) timp de 60 min în mediul acid (pH=2,5) a fost determinată eficiența de degradare de 88 % și eficiența de oxidare/mineralizare de 83 %. La fel, s-au calculat constantele de viteză în funcție de parametrii fizico-chimici optimizați.
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    Optimizarea procesului de oxidare catalitică a contaminanților emergenți farmaceutici (amoxicilina) în soluție apoasă [Articol]
    (US Cahul, 2020-06-05) Mocanu, Larisa; Duca, Gheorghe; Gonța, Maria; Matveevici, Vera; Porubin-Schimbător, Veronica
    Acest articol descrie un studiu de oxidare al amoxicilinei cu reagentul Fenton în mediul acid. Deoarece aceste reziduuri medicamentoase sunt ne-biodegradabile, oxidarea catalitică ar putea fi o alternativă de tratament foarte eficientă. Obiectivul principal al acestei cercetări a fost optimizarea parametrilor ce influențează procesul de oxidare al AMX. Au fost realizate mai multe studii experimentale pentru a determina efectul degradării/ mineralizării și concentrațiile optime de H2O2 și catalizator. Concentrațiile inițiale ale substanțelor reactante au fost variate în intervalul: 0,01 – 0,3 mM pentru Fe (II) și 1 – 5 mM pentru H2O2. PH-ul a fost ajustat la valoarea 2,2 utilizând H2SO4 de 0,1 N. În rezultatul cercetărilor de laborator, s-a constatat că raportul dintre Fe2+: H2O2: AMX este de 1:10:2. S-a ajuns la concluzia că efectul de răspuns al fiecărei variabile independente depinde de valoarea celeilalte, datorită existenței interacțiunilor încrucișate. Astfel, oricare dintre parametrii studiați ar putea influența pozitiv sau negativ degradarea amoxicilinei. Ca urmare a procesului de optimizăre al parametrilor fizico–chimici, s-a obținut că rata maximă de mineralizare/ oxidare a amoxocilinei a fost de 99%, iar rata de degradare a AMX– 88%.
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    The diminishing of the content of textile direct dyes and auxiliary compounds during their catalytic oxidation [Articol]
    (2014) Gonța, Maria; Duca, Gheorghe; Matveevici, Vera; Mocanu, Larisa
    Advanced oxidation methods of organic compounds lead to their partial mineralization and increase of the adsorption process efficiency on the surface of oxidized activated carbon. We have studied the oxidation process using model solutions containing mixture of dye direct brown (DB), ethylene glycol (EGL) and sodium lauryl sulfate (SLS) under the action of Fenton reagent, in the presence and absence of UV irradiation or under the action of electric current(in the electrochemical cell). The same studies were performed by replacing the iron (II) ion with titanium dioxide. We have found that the degree of oxidation and mineralization increases by photocatalytic oxidation and decreases the concentration of organic compounds. Due to the oxidation of dye molecules and other auxiliary components, by strong oxidation ability of free OH* radicals, which evolve to the formation of carbon dioxide, water and low molecular organic compounds (alcohols, ketones, organic acids) are forming. The decrease of the concentration of mixture of organic compounds (for the values of COD-Cr) depends on the nature of catalysts and the presence of electric current. The degree of oxidation is greater in the presence of iron (II) ions than in the presence of titanium dioxide after oxidation of the mixture of organic compounds with hydrogen peroxide in model solutions. This is explained by the fact that UV irradiation increases the concentration of free OH* radicals as iron ions further decompose hydrogen peroxide, but in the presence of titanium dioxide, the leading band electrons are accepted by free OH* radicals, converting these radicals to ions, as shown in the mechanism by Garcia J., et al. This leads to a decrease of the concentration of OH* radicals in model solution and reducing the effect of oxidation, respectively. On the contrary, in the presence of electric current electrons are accepted by the electrode, and the OH* radicals concentration does not decrease, but increases, and this leads to the enhancement of the oxidation effect and mineralization of organic compounds.
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    Regional climate change and surface waters [Articol]
    (2019) Duca, Gheorghe; Nedealcov, Maria; Travin, Serghei; Gladchi, Viorica
    The actual period marred by the global warming requires expanding our knowledge on the regional particularities of climate changes manifestations as consequences of global climatic changes. It was stated that within the limits of Republic of Moldova’s territory the pace of warming is much more accelerated than the global one. These consequences, in their turn, had led to the increase in degree of evaporation of surface waters, which had conditioned the doubling of still water’s pollution in the region (Lake Beleu). We consider that the obtained results could contribute to the adequate management of water resources in the new climatic conditions.
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    Self-purification of aquatic media from hexachlorocyclohexane in a radical process [Articol]
    (2019) Travin, Serghei; Duca, Gheorghe; Gladchi, Viorica
    It is known, that highly toxic pesticide hexachlorocyclohexane (HCH) is resistant to decomposition and has a long-term accumulating capacity. Nevertheless, it undergoes complete degradation in reactions with hydroxyl radicals in Fenton-like systems. The goal of this work was to study the influence of HCH on the processes of radical self-purification of water bodies and to explain the mechanisms of chemical transformation of substances occurring in natural waters, as well as to reveal the kinetic characteristics of the processes of radical self-purification of water bodies. It was found, that HCH plays a dual role for aquatic ecosystems – it is not only a scavenger of free radicals, but also an additional initiator. Under the influence of light in the surface layer of water, HCH generates radicals, thus contributing to the self-purification processes.
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    Soluţii pentru prevenirea şi diminuarea consecinţelor inundaţiilor [Articol]
    (2010) Duca, Gheorghe; Furdui, Teodor; Melniciuc, Orest; Zubcov, Elena; Gladchi, Viorica; Moraru, Constantin; Bogdevici, Oleg; Arnăut, Nicolae; Bujac, Victor
    The danger of floods is very up to date for the Republic of Moldova, so, two types of flood are characteristic: transboundary, caused by Dniester and Prut rivers, and local, caused by discharges of small streams, lakes, ponds. A group of experts from the Academy of Sciences of Moldova developed solutions to prevent damages caused by triggering floods. Among these are: the creation of National center of flood monitoring; the assessment of flood areas and the liable to inundation potential of Dniester and Prut rivers and small streams; the elaboration of “Scheme of protection of populated localities against flood”; the regular water sampling in flood areas to monitor the state of pollution; the implementation of flash flood model; the agreement between Ukraine-Republic of Moldova-Romania on monitoring, forecasting and sustainable exploitation of aquatic ecosystems etc.