Photocatalytic processes as a potential solution for plastic waste management

Plastics have become a critical environmental problem due to their widespread use, high physico-chemical stability and the inefficiency of wastewater treatments. Despite the efforts to reduce production and to increase reuse and recycling, the current strategies for plastic waste treatment are not suitable to handle with the growing demand of plastics and the concomitant waste in an environmentally friendly manner. Herein, we review the existing strategies for the treatment of plastic waste, highlighting photocatalytic processes as a potential solution for the degradation of plastics. The possibility of incorporating photocatalysts to plastics during the production process could enhance their light-activated biodegradability. Parallelly, photocatalysts can be employed during waste treatment processes of non-biodegradable stable plastics. The scarcely studied factors affecting plastic photocatalytic degradation, namely catalyst type, reactor configuration, and radiation source (intensity and wavelength), are discussed, highlighting the role that photocatalytic processes can play in the future of plastic management. Finally, relevant quantification methods for measuring the photo-degradation of plastics are overviewed. We believe that photocatalysis can be an environmentally friendly strategy both to increase the biodegradability of plastics and to treat plastic waste. With this novel comprehensive overview, we hope to stimulate further research and innovation in this field.Xunta de Galicia | Ref. ED481B 2019/091Universidade de Vigo/CISU

GO-TiO2 as a highly performant photocatalyst maximized by proper parameters selection

The synthesis and characterization of novel graphene oxide coupled to TiO2 (GO-TiO2) was carried out in order to better understand the performance of this photocatalyst, when compared to well-known TiO2 (P25) from Degussa. Thus, its physical-chemical characterization (FTIR, XRD, N2 isotherms and electrochemical measurements) describes high porosity, suitable charge and high electron mobility, which enhance pollutant degradation. In addition, the importance of the reactor set up was highlighted, testing the effect of both the irradiated area and distance between lamp and bulb solution. Under optimal conditions, the model drug methylthioninium chloride (MC) was degraded and several parameters were assessed, such as the water matrix and the catalyst reutilization, a possibility given the addition of H2O2. The results in terms of energy consumption compete with those attained for the treatment of this model pollutant, opening a path for further research.Xunta de Galicia | Ref. ED481B 2019/091Ministerio de Ciencia e Innovación | Ref. PID2020-113667GB-I0

Fluoride-doped TiO2 photocatalyst with enhanced activity for stable pollutant degradation

Fluoride-doped TiO2 (F-TiO2) was synthesized by an efficient and simple one-step synthesis and successfully used for the UV-photo-degradation of the toxic and stable pollutants methylene blue (MB) and bisphenol A (BPA). Initially, the synthesized catalyst was characterized and compared to untreated TiO2 (P25 Degussa) by different physical–chemical analyses such as XRD, band gap calculation, SEM, EDS, FITR, ECSA, or EIS. F-TiO2 defeated commercial TiO2, and almost complete pollutant removal was achieved within 30 min. The energy consumption was reduced as a result of the suitable reactor set-up, which reduced light scattering, and by the application of a long-pulse radiation procedure, where the lamp was switched off during periods where the radical degradation continued. This enhanced the overall photocatalysis process performance. Under these conditions, 80% of MB removal was attained within 15 min radiation with an energy consumption of only 0.070 Wh min−1, demonstrating a much better efficiency when compared to previously reported data. The catalyst was reusable, and its performance can be improved by the addition of H2O2. The results were validated by BPA degradation and the treatment of real wastewaters with both pollutants. The results were so encouraging that a scale-up reactor has been proposed for future studies.Xunta de Galicia | Ref. ED481B 2019/091Xunta de Galicia | Ref. ED431C 2021-43Ministerio de Ciencia e Innovación | Ref. PCI2022-132941Ministerio de Ciencia e Innovación | Ref. PID2020- 113667GB-I0

Magnetic TiO2/Fe3O4-chitosan beads: a highly efficient and reusable catalyst for photo-electro-fenton process

Heterogeneous photo-electro-Fenton process is an attractive technology for the removal of recalcitrant pollutants. To better exploit the presence of an irradiation source, a bifunctional catalyst with TiO2 nanoparticles embedded into an iron–chitosan matrix was developed. The catalytic activity of the catalyst was improved by the optimization of the loaded TiO2content. The prepared composite catalysts based on TiO2, Fe3O4 and chitosan were called TiO2/Fe3O4-CS beads. The best catalyst with an optimal ratio TiO2/Fe = 2 exhibited a high efficiency inthe degradation and mineralization of chlordimeform (CDM) insecticide. Under the optimum conditions (concentration of catalyst equal to 1 g L−1 and applied current intensity equal to 70 mA), a real effluent doped with 30 mg L−1 of CDM was efficiently treated, leading to 80.8 ± 1.9% TOC reduction after 6 h of treatment, with total removal of CDM after only 1 h.The generated carboxylic acids and minerals wereidentified and quantified. Furthermore, the stability and reusability of the developed catalyst was examined, and an insignificant reduction in catalytic activity was noticed forfour consecutive cycles of the photo-electro-Fenton process. Analyses using SEM, XRD and VSM showed a good stability of the physicochemical properties of the catalyst after use.Xunta de Galicia | Ref. ED481B 2019/091Ministerio de Ciencia e Innovación | Ref. PID2020-113667GB-I00 464Universidad de Kairouan, Túnez | Ref. UR16ES0

Nano-zero-valent particles synthesized with agroindustry wastes for pesticide degradation under real conditions

Nano-zero-valent particles (NZVP) had exhibited high degradation activity. NZVP synthesized from agroindustry residues align with circular economy principles. They generate hydroxyl radicals (4.6 µM) that effectively degraded chlorpyrifos-methyl pesticide under real conditions. Bimetallic NZVP, specifically NZVP-Fe:Mn and NZVP-Fe:Ag, show superior pesticide degradation. The metal ratio within NZVP influences their activity (optimal at 0.12:0.12 mM and 0.12:0.19 mM for respectively, NZVP-Fe:Mn and NZVP-Fe:Ag). NZVP characterization includes TEM, SEM-EDS, PZC, FTIR, XRD, and electrochemical analysis, confirming their acid nature, favorable electrochemical behavior, and uniform metal distribution. The impact of different natural extracts on NZVP synthesis and pesticide degradation was explained through extensive extract characterization, revealing the presence of altering pro-oxidants and scavenger species. Blueberry pruning extract yields the highest pesticide degradation (85% in 5 min) due to its stronger antioxidant activity and lower scavenger compound content. NZVP demonstrates efficacy across various pH ranges. Real wastewater samples were treated under optimal conditions, resulting in a pesticide degradation efficiency of approximately 60% within 5 min. The most effective approach for enhancing the treatment process involved the sequential addition of reagents, as opposed to the conventional method of increasing reagent concentrationXunta de Galicia | Ref. ED481B 2019/091Fundação para a Ciência e a Tecnologia | Ref. UIDB/50006/2020Fundação para a Ciência e a Tecnologia | Ref. UIDP/50006/2020Fundação para a Ciência e a Tecnologia | Ref. LA/P/0008/2020Ministerio de Ciencia e Innovación | Ref. PCI2022-132941Universidade de Vigo/CISUGFundação para a Ciência e a Tecnologia | Ref. CEECIND/02702/201

Novas perspectivas na aplicación dos Procesos de Oxidación Avanzada

The Advanced Oxidation Processes (AOPs) have been widely studied as they can degrade many types of organic contaminants, due to the action of the hydroxyl radicals which are generated in this kind of processes. Previous studies performed in the BIOSUV group demonstrate the AOPs are an efficient alternative for the remediation of different effluents. In the current context, this thesis is going to be focused in the use of the AOPs in the treatment of effluents with high organic load (such as the winery solutions), or with emerging contaminants (such as pesticides, drugs or ionic liquids). Contaminated soils would be also treated. It is proposed the study of different AOPs: i) The Fenton process, in which the hydroxyl radicals are obtained due to the reaction between iron and hydrogen peroxide, ii) the electro-Fenton process where an electric field is applied in order to generate the hydrogen peroxide and to favor the degradation mechanism, iii) the photo-Fenton process, carried out with an external ultraviolet radiation, iv) the photo-electro-Fenton process which combines the aforementioned processes. The effect of the working parameters in the AOPs would be studied, in order to increase the production of hydroxyl radicals and, undeniably, the degradation of the contaminants. Therefore, different reactor´s configurations would be used to maximize the processes´ efficiency (choosing between different reactor´s size, kind of electrodes, radiation...). These studies would allow the optimization of the working conditions (such as the concentration of catalyst, voltage…), improving all the processes. Furthermore, another line of investigation would be based on the development of new heterogeneous iron catalyst, which would be useful for working in batch and continuous mode, avoiding the detected problems of working with homogeneous catalyst. On the other hand, the viability of the ElectroKinetic-Fenton treatments for the remediation of soils will be evaluated. In this kind of experiments it is important to know how the different species move in the soil as well as how the contaminant is degraded during its treatment in the soil. For quantifying the degradation of the different contaminants, the implementation of the analytic techniques would be done (such as spectrophotometry, liquid and gas chromatography, TOC, COD and hydroxyl radicals measurements…) as well as the usage of toxicity measurements (Microtox assays, phytotoxicity …). Moreover, the viability of the processes would be studied.Los Procesos de Oxidación Avanzada (POA) han sido ampliamente estudiados debido a su capacidad de degradar diversos tipos de contaminantes orgánicos, gracias a la acción de los radicales hidroxilo generados en este tipo de procesos. Estudios previos realizados por el grupo BIOSUV, señalan que este tipo de procesos son una alternativa eficiente para la remediación de efluentes de distinta tipología. En este contexto, esta Tesis se centrará en el uso de los POA para el tratamiento de efluentes con alta carga orgánica (como los residuos procedentes de la industria vitivinícola) y con contaminantes emergentes (como los pesticidas, medicamentos o líquidos iónicos) así como en suelos contaminados. Se plantea el estudio de distintos POAs: i) Proceso Fenton, en el que se obtienen radicales hidroxilo mediante la descomposición de peróxido de hidrógeno catalizada por hierro (II), ii) el proceso electro-Fenton, en el que se aplica un campo eléctrico para generar el peróxido de hidrógeno y favorecer los mecanismos de degradación, iii) el proceso foto-Fenton, que se lleva a cabo con una fuente de radiación ultravioleta externa, iv) el proceso Foto-Electro-Fenton que es una combinación de los anteriores. Para los distintos POAs, se estudiará el efecto de los diferentes parámetros operacionales, con el objeto de aumentar la producción de los radicales hidroxilo, y por ende, la degradación de los contaminantes a tratar. Por ello, se prevé trabajar con varias configuraciones de reactor que ayuden a maximizar la eficacia de los procesos (eligiendo el tamaño, los electrodos, el tipo de radiación…). Estos estudios permitirán optimizar las condiciones de trabajo (cantidad de catalizador, voltaje…) mejorando la eficiencia de los procesos estudiados. Asimismo, se abrirá una línea de trabajo orientada al desarrollo de catalizadores heterogéneos de hierro, que permitirá trabajar tanto en batch como en continuo, evitando los problemas detectados en la catálisis homogénea. Paralelamente, se evaluará la viabilidad de la técnica Electrocinética-Fenton para la remediación de suelos contaminados. En estos experimentos es de vital importancia determinar la movilidad en los suelos de las distintas especies presentes e identificar los mecanismos que tienen lugar en el suelo a lo largo de su tratamiento. Para la cuantificación de la degradación de los distintos contaminantes, será necesaria la puesta a punto de las técnicas analíticas a utilizar (espectrofotometría, cromatografía líquida y gaseosa, medidas de COT, DQO, radicales hidroxilo…) y de toxicidad (Microtox, estudios de fitotoxicidad…). Asimismo se llevarán a cabo estudios de viabilidad de los distintos procesos.Os Procesos de Oxidación Avanzada (POAs) están a ser amplamente estudados debido a súa capacidade de degradar diversos tipos de contaminantes orgánicos, grazas a acción dos radicais hidroxilo que son xerados neste tipo de procesos. Estudos previos feitos no grupo BIOSUV, demostran que este tipo de procesos son unha alternativa eficiente para a remediación de efluentes de distinta tipoloxía. Neste contexto, a tese centrarase no uso dos POAs para o tratamento de efluentes con alta carga orgánica (como os residuos procedentes da industria vitivinícola), o con contaminantes emerxentes ( como os pesticidas, medicamentos ou líquidos iónicos). Tamén trataranse chans contaminados. Planease o estudio dos distintos POAs: i) Proceso Fenton, no que se obteñen radicais hidroxilo mediante a acción do peróxido de hidróxeno e ferro, ii) o proceso electro-Fenton, no que se aplica un campo eléctrico para xerar o peróxido de hidróxeno e favorecer os mecanismos de degradación, iii) o proceso foto-Fento, que lévase a cabo cunha fonte de radiación ultravioleta externa, iv) o proceso Foto-Electro-Fenton, que é unha combinación dos anteriores. Para os distintos POAs, estudarase o efecto dos diferentes parámetros operacionais, co obxectivo de aumentar a produción dos radicais hidroxilo, e por ende, a degradación dos contaminantes a tratar. Por iso, se prevé traballar con varias configuracións de reactor que axuden a maximizar a eficacia dos procesos (elixindo o tamaño, os eléctrodos, o tipo de radiación...). Estes estudios permitirán optimizar as condicións de traballo (cantidade de catalizador, voltaxe...) mellorando a eficiencia dos procesos estudados. Así mesmo, abrirase unha liña de traballo orientada o desenvolvemento de catalizadores heteroxéneos de ferro, que permitirá traballar tanto en batch como en continuo, evitando os problemas detectados na catálise homoxénea. Paralelamente, evaluarase a viabilidade das técnicas Electrocinética-Fenton para a remediación de devanditos chans contaminados. Nestes experimentos é de vital importancia determinar a mobilidade nos chans das distintas especies presentes e identificar os mecanismos que teñen lugar no chan o largo do seu tratamento. Para a cuantificación da degradación dos distintos contaminantes será necesaria a posta a punto das técnicas analíticas a utilizar (espectrofotometría, cromatografía líquida e gasosa, medidas de COT, DQO, radicais hidroxilo) e de toxicidade (Microtox, estudos de fitotoxicidade…). Así mesmo levaranse a cabo estudos de viabilidade dos distintos procesos.Ministerio de Economía y Competitividad de España | Ref. CTM2014-52471Ministerio de Economía y Competitividad de España | Ref. BES-2015.071317Xunta de Galicia | Ref. ED431C 2017/47Xunta de Galicia | Ref. GRC 2013/00

Iron-loaded catalytic silicate adsorbents: synthesis, characterization, electroregeneration and application for continuous removal of 1-butylpyridinium chloride

This research proposes the application of iron-loaded sepiolite (S-Fe) as a catalytic adsorbent for the unreported 1-butylpyridinium chloride ([bpy] Cl) treatment in an aqueous medium. Initially, sepiolite was selected as an inexpensive and efficacious adsorbent for [bpy] Cl elimination. After that, sepiolite was loaded with iron for the subsequent electro-Fenton (EF) regeneration treatment. Once kinetic and isotherm studies were performed, providing respectively almost instantaneous adsorption (20 min) and an uptake of 22.85 mg/g, [bpy] Cl adsorption onto S-Fe was studied in continuous mode. The obtained breakthrough curve was analyzed using three standard breakthrough models, being Yoon–Nelson and Thomas the most suitable adjustments. Afterwards, S-Fe regeneration by the EF process was conducted using this iron-loaded silicate material as a heterogeneous catalyst. Under optimized operational conditions (current intensity 300 mA and Na2SO4 0.3 M), complete adsorbent regeneration was achieved in 10 h. The total mineralization of [bpy] Cl was reached within 24 h and among seven carboxylic acids detected, oxalic and acetic acids seem to be the primary carboxylic acids produced by [bpy] Cl degradation. Finally, S-Fe was efficiently used in four consecutive adsorption–regeneration cycles without a noticeable reduction in its adsorption capacity, opening a path for future uses.European Regional Development Fund | Ref. CTQ2017-90659-REDTXunta de Galicia | Ref. ED481B 2019/091Ministerio de Ciencia, Innovación y Universidades | Ref. CTM2017-87326-