Water Depollution Research Articles

TiO2 Doped with Noble Metals as an Efficient Solution for the Photodegradation of Hazardous Organic Water Pollutants at Ambient Conditions

This work highlights new insights into the performance of TiO2 doped with noble metal catalysts for the photocatalytic degradation of organic water pollutants. Different samples of titanium dioxide doped with noble metals (Au and Pd) were successfully synthesized via incipient wet impregnation (IWI) and ultrasound-assisted impregnation (US) methods. X-ray diffraction, scanning electron microscopy and UV-Vis reflectance spectroscopy were used for the characterization of the obtained materials. Their photocatalytic efficiency was investigated in aqueous suspension thorough a series of laboratory tests performed under ultraviolet (UV-A) irradiation conditions using 2,4 dinitrophenol (2,4 DNP) as a target molecule. The results clearly show that the method used for the catalyst synthesis affects its photocatalytic activity. It was found that the samples prepared by the IWI method exhibited high photocatalytic activity, and the removal rate obtained with TiO2-Pd/IWI was higher than that found for TiO2-Au/IWI. Furthermore, for the best catalyst, some extra photocatalytic experiments were conducted with rhodamine 6G (R6G), a highly stable molecule with a very different chemical structure to 2,4 DNP, in order to check the reactivity of this material. Moreover, the recycling experiments carried out with TiO2-Pd/IWI clearly demonstrated the high photocatalytic stability of this material for the degradation of 2,4 DNP. All of the collected data confirmed the interesting photocatalytic potential of the selected catalyst in the elimination of organic pollutants with no obvious change in its reactivity after four reaction cycles, which is very promising for promoting future applications in water depollution.

PRELIMINARY ANALYSES OF THE EFFICIENCY OF SUSTAINABLE FILTERS AND HYDROELETRIC POTENTIAL FOR A CLEAN ENERGY GENERATION AND WATER DEPOLLUTION SYSTEM

In last decades, water pollution has become more pronounced on all rivers in Latin America, Africa and Asia. Thus, it is estimated that the deterioration of water quality will extend further over the coming decades, increasing threats to human health, environment and sustainable development. Simultaneously, it has been observed a depletion of non-renewable energetic sources and its increasing replacement by renewable sources. Therefore, the United Nations (UN) has been setting goals regarding sustainable development for the countries. Thus, the present study aimed to create and design a mechanism that integrates clean energy generation and water depollution from small and medium-sized streams by using agro-industrial waste. For this, it was necessary to survey the theoretical framework besides the hydrological study of Pinhalzinho II watershed, which was chosen for the simulation. Thus, it was started the design of the hydroelectric microcentral coupled to a sustainable water purification system using the softwares: AutoCAD© and SketchUp 3D©. In addition, the stream flow was determined and its energy potential was calculated in order to estimate the amount of energy that could be generated by the system. Then, laboratory scale filters were constructed from sugarcane bagasse and cassava peel for efficiency analyses. Finally, the upstream (raw water) and downstream (after filtering) water samples were analyzed and their parameter values determined. After data treatment, it was found that the results were not satisfactory; conversely, they showed a reduction in raw water quality, achieving efficiency only for the thermotolerant coliforms parameter. Nevertheless, regarding the hydroelectric microcentral project and the hydroenergetic potential of the stream, the results were promising.

Plasmonic Materials: Opportunities and Challenges on Reticular Chemistry for Photocatalytic Applications

AbstractSolar‐light harvesting materials currently represent a hot topic in catalysis due to the several applications where they can be used. Among the recent strategies to enhance the photocatalytic performance of semiconductor materials, plasmonic metals are trending. Coupling plasmonic metal nanoparticles with a semiconductor material can give unique synergistic effects and properties. Especially when reticular materials, like metal organic frameworks, are used to generate these plasmonic nanocomposites. Herein, a brief introduction to the localized surface plasmon resonance and reticular materials design and fabrication is given. Also, the advantages of plasmonic with reticular nanostructures are discussed. The following highlights summarize recent advances in sunlight‐driven plasmonic reactions (CO2 photoreduction, water depollution, gas sensing, and optical reactions). Theoretical and experimental approaches are discussed, regarding mechanistic phenomena of nanocomposites with reticular materials and surface plasmon metals. A proper discussion and perspective of the remaining challenges and future opportunities for plasmonic metals with reticular materials in the field of photocatalysis is given in the overview and conclusion.

Enhancement of the photocatalytic activity of decatungstate, W10O324−, for the oxidation of sulfasalazine/sulfapyridine in the presence of hydrogen peroxide

The degradations of sulfasalazine and also sulfapyridine have been investigated by using the sodium decatungstate Na4W10O32 as a photocatalyst in the presence of hydrogen peroxide as a sacrifial agent. The selective irradiation of decatungstate, W10O324−, in the presence of the pollutants at 365 nm and at pH = 4.0 leads to the reduction of hydrogen peroxide via a Fenton like reaction involving the reduced species, W10O325-. Such process represents an efficient way for the formation of the highly reactive species, namely the hydroxyl radicals. The process appears then to be highly efficient for the oxidation of the pollutants sulfasalazine and sulfapyridine. Under our experimental conditions, the process was optimized in terms of concentrations of the photocatalyst, hydrogen peroxide and pollutant concentrations and also in term of pH. For both pollutants, the analysis of the generated by-products, using HPLC/MS, shows that the degradation proceeds primarily through three and common chemical processes: i) hydroxylation ii) desulfurization and iii) scission at the azo group -N = N-. The attack of the hydroxyl radical is clearly the main species for the degradation processes. As clearly demonstrated by the TOC experiments, the combination of W10O324−/H2O2/hν system permitted a total mineralization of the solution indicating its high efficiency for the a potential application of water depollution.

Water Depollution and Photo-Detoxification by Means of TiO2: Fluoroquinolone Antibiotics as a Case Study

Photocatalysis by semiconductors is considered one of the most promising advanced oxidation processes (AOPs) and TiO2 is the most well-studied material for the removal of contaminants from the aquatic system. Over the last 20 years, pharmaceuticals have been the most investigated pollutants. They re-enter the environment almost unmodified or slightly metabolized, especially in the aquatic environment, since the traditional urban wastewater treatment plants (WWTPs) are not able to abate them. Due to their continuous input, persistence in the environment, and unpleasant effects even at low concentrations, drugs are considered contaminants of emerging concern (ECs). Among these, we chose fluoroquinolone (FQ) antibiotics as an environmental probe for assessing the role of TiO2 photocatalysis in the degradation of recalcitrant pollutants under environmental conditions and detoxification of surface waters and wastewaters. Due to their widespread diffusion, their presence in the list of the most persistent pollutants, and because they have been deeply investigated and their multiform photochemistry is well-known, they are able to supply rich information, both chemical and toxicological, on all key steps of the oxidative degradation process. The present review article explores, in a non-exhaustive way, the relationship among pollution, toxicity and remediation through titanium dioxide photocatalysis, with particular attention to the toxicological aspect. By using FQs as the probe, in depth indications about the different phases of the process were obtained, and the results reported in this paper may be useful in the improvement of large-scale applications of this technology, and—through generally valid methods—they could be deployed to other pharmaceuticals and emerging recalcitrant contaminants.

Research on the Efficiency of Testing a New Adsorbent Material with Cellulose Structure for the Depollution of Waste Water

The global concern in wastewater recycling technologies has grown steadily since the early 1990s and is gaining more and more interest due to the increase in water supply needs. This growing need affects many global regions and leads to an increase in the strictness of environmental regulation, both in developing and developed countries. Many countries, cities and local governments are trying to recycle wastewater as a potential source of water for various uses, especially non-potable uses, such as land use, water for toilets and industrial processes. Analysts and statisticians around the world are trying to provide a perspective on an industry that is poised to see significant developments in the next decade. The researches summarize the experimental tests carried out using a new cellulosic adsorbent material to purify the wastewater resulted from the industrial processes for leather manufacturing. The study highlights the influence of the pH used for the wastewater depollution. The tracked and measured parameters include the pH, chemical oxygen demand, biochemical oxygen demand, total suspended solids, ammoniac nitrogen, organic compounds extractable in organic solvents and the solid residue adsorbed by the material. The obtained values were discussed in concordance with the national legislation for wastewater treatment and the levels accepted for releasing the used water in the surface waters.

Optimization by Using Response Surface Methodology of the Preparation from Plantain Spike of a Micro-/Mesoporous Activated Carbon Designed for Removal of Dyes in Aqueous Solution

Response surface methodology based on central composite design was used as a tool to optimize the preparation of micro-/mesoporous activated carbon from plantain spike. The impact of three variables: activation temperature, activation time, and H3PO4 impregnation ratio, were evaluated on the iodine number and the methylene blue (MB) index according to the model-determined conditions. These three variables have been extensively studied using analysis of variance to assess their significance. Each response was described by a second-order regression equation showing good agreement between the predicted and the experimental data as the adjusted correlation coefficients were greater than 0.80. The multi-response optimized conditions have been set at the temperature of 480 °C, the activation time of 113 min, and the impregnation ratio of 3.34/1 (w/w). The activated carbon prepared in these conditions has a specific surface area of 896 m2/g with micro- and mesopore volumes of 34% and 66%, respectively. Water depollution capacity of this activated carbon evaluated by adsorption of MB and iodine was 206 mg/g and 927 mg/g, respectively.

Design and engineering of layered double hydroxide based catalysts for water depollution by advanced oxidation processes: a review

Various strategies to design LDH catalysts for advanced oxidation processes.

Exploration of a novel Type II 1D-ZnO nanorods/BiVO4 heterojunction photocatalyst for water depollution

In this study, we reported on the successful fabrication of a novel heterojunction photocatalyst (in particulate system) with a Type II band alignment between 1D-ZnO nanorods and BiVO4 nanocrystals. Pristine 1D-ZnO nanorods and BiVO4 nanocrystals were first fabricated through hydrothermal reaction followed by heterojunction formation via the wet chemical reaction. The 1D-ZnO/xBiVO4 heterojunction photocatalyst (x=weight ratio of BiVO4 in g) that found optimum when x=0.08g was used for the degradation of salicylic acid (SA) and Reactive Black 5 (RB5) resulting in high pseudo-first-order reaction rate constants of 0.0049min−1 and 0.0132min−1, respectively. Electrochemical studies proved that the 1D-ZnO/0.08BiVO4 heterojunction photocatalyst demonstrated a fast charge mobility and the most efficient photogenerated charge carriers separation among other heterojunction samples as analysed from PL spectra. Besides, UV–vis spectroscopic measurement and optical characterisation showed that the improved photoactivity in 1D-ZnO/BiVO4 is attributed to the formation of a Type II heterojunction staggered arrangement that enables a broader visible-light harvesting ability. Finally, a postulation photocatalytic mechanism was proposed based on the theoretical band alignment diagram between the 1D-ZnO nanorods and BiVO4 nanocrystals as well as portraying the fundamental charge carriers transfer within the 1D-ZnO/BiVO4 heterojunction photocatalyst.

Ambient temperature ZrO2-doped TiO2 crystalline photocatalysts: Highly efficient powders and films for water depollution

In this paper, several TiO2 materials doped with zirconia precursor (0.7, 1.4, 1.6 and 2.0 mol%) were synthesized by an easy aqueous sol-gel synthesis at ambient temperature. This method consists in the peptization of the TiO2 colloid in presence of HNO3. The corresponding pure TiO2 material was also synthesized for comparison. The performances and the physico-chemical properties of these materials were compared to the well-known Evonik P25 photocatalyst.The physico-chemical characterizations showed that nano-crystalline anatase-brookite particles were produced with the sol-gel process, with higher specific surface area than P25 (∼200 m2 g-1 vs. 47 m2 g-1). All samples presented a higher visible absorption than P25. The XPS spectra showed that all the samples were doped with nitrogen and that mixed TiO2–ZrO2 oxide materials were obtained when doping with zirconia precursor.Photoactivity was evaluated through the degradation of p-nitrophenol in water. On the one hand, under UV/visible light, the ZrO2 doping increased the degradation efficiency of the pure TiO2 catalyst due to a better charge separation in the mixed TiO2–ZrO2 oxides. The activity of the sample with the highest dopant content was even higher than the one of P25. On the other hand, under visible light, all samples were much more efficient than P25. This activity shift towards visible range was due to the N-doping of the catalysts, with a slight improvement for the doped ones.Finally, the feasibility of producing films starting from an aqueous suspension of the photocatalyst was assessed on P25, pure TiO2 and the best doped material. The photoactivity of these films, evaluated on the degradation of methylene blue under UV-A light, showed that the sample with the highest dopant concentration had an efficiency 4 times higher than pure TiO2 and 20 times higher than P25.

Nanomaterials applied for heavy metals removal from wastewater

In the past years, nanotechnology has been studied and it proved that is one of the advanced ways for toxic compounds removal from wastewater. In this paper we focus on nanomaterials used for treatment of wastewater containing heavy metals. Nanoparticles have very high and specific adsorption capacity being applied in water depollution, remediation and treatment process. The depollution methods based on nanomaterials could be more cost-effective, less time and energy consuming, generating no or less waste in comparison with conventional methods. The aim of this review is to summarize the applications of nanoadsorbants within heavy metals depollution methods.

Textile Wastewater Purification Using an Elaborated Biosorbent Hybrid Material (Luffa–Cylindrica–Zinc Oxide) Assisted by Alternating Current

This paper aims to synthesize hybrid materials with high pollutant-uptake capacity and low costbased based on Luffa cylindrica (L.C) and different percentage of Zn2+ in the presence and absence of alternating current (AC). Physico-chemical, morphological and structural characterizations of the hybrid materials were performed by Boehm method, point zero charge (pHpzc), infrared characterizations (IR), scanning electron microscopy (SEM), energy–dispersive spectroscopyand and X-ray photoelectron spectroscopy. The efficiency of the designed hybrid materials was optimized based on their performance in water depollution. Methylene blue (MB) and industrial textile wastewater were the investigated pollutants models. IR characterizations confirmed the fixation of Zn2+ onto the L.C by the creation of Zn-OH, Zn-O and Zn-O-C bonds. Boehm titration showed that the fixation of Zn2+ onto L.C is accompanied by an increase of the basic functions of its surface and subsequently an increase in the pHpzc. SEM results confirmed the fixation of Zn2+ onto the L.C coupling AC with biosorption showed an increase in the adsorbed amount of MB and speed when adding the 4% of Zn2+ compared to the pure L.C the Qm shifted from 3.22 to 9.84 and 8.81 mg/g, respectively, for hybrid materials synthesized under AC, in absence of AC and pure L.C.

State of the Art and Prospects in Metal-Organic Framework (MOF)-Based and MOF-Derived Nanocatalysis.

Metal-organic framework (MOF) nanoparticles, also called porous coordination polymers, are a major part of nanomaterials science, and their role in catalysis is becoming central. The extraordinary variability and richness of their structures afford engineering synergies between the metal nodes, functional linkers, encapsulated substrates, or nanoparticles for multiple and selective heterogeneous interactions and activations in these MOF-based nanocatalysts. Pyrolysis of MOF-nanoparticle composites forms highly porous N- or P-doped graphitized MOF-derived nanomaterials that are increasingly used as efficient catalysts especially in electro- and photocatalysis. This review first briefly summarizes this background of MOF nanoparticle catalysis and then comprehensively reviews the fast-growing literature reported during the last years. The major parts are catalysis of organic and molecular reactions, electrocatalysis, photocatalysis, and views of prospects. Major challenges of our society are addressed using these well-defined heterogeneous catalysts in the fields of synthesis, energy, and environment. In spite of the many achievements, enormous progress is still necessary to improve our understanding of the processes involved beyond the proof-of-concept, particularly for selective methane oxidation, hydrogen production, water splitting, CO2 reduction to methanol, nitrogen fixation, and water depollution.

Solar-driven advanced oxidation process catalyzed by metal–organic frameworks for water depollution

Phosphonate-based MOF materials namely, STA-12(M) (M = Mn, Fe, Co, Ni), show photocatalytic activity for the degradation of methylene blue (MB) and methyl Orange (MO) from aqueous solution under natural sunlight irradiation. Thus, photo-Fenton oxidative discoloration of dyes have been surveyed by H2O2 catalyzed with the STA-12(M). The degradation of the dyes, appears to be faster with STA-12(Fe) than other synthesized MOFs. The reaction is first order with respect to MO and MB dyes and the synergistic index in the STA-12(Fe)/sunlight/H2O2system reached as high as 431%. Mineralization of dyes was discussed by spectroscopic and TOC measurement. Besides, the efficiency of STA-12(Fe) used in photo-Fenton process was attentively investigated through the characterization of reactive radicals, the stability and reusability of the photocatalyst, also the effect of operational parameters such as H2O2 dosage, solution pH and initial dye concentration. This work demonstrates the first example of facilitating photo-Fenton excitation of H2O2 via phosphonate based metal organic frameworks as photocatalysts and explained a new opportunity for sunlight-induced photocatalytic environmental remediation and protection.

Lead removal from aqueous solution by means of integral natural clays honeycomb monoliths.

Different natural Moroccan clays were used as adsorbents for the removal of lead from aqueous solution. The study was performed not only employing the starting clays in the form of powder but also after their extrusion as honeycomb monoliths, this representing the major novelty of this work respect to the current state-of-art. The experiments were done in batch conditions with continuous stirring and using a recirculated flow, respectively. In addition to an exhaustive characterization of the clays by means of X-ray fluorescence, X-ray diffraction, thermogravimetric analysis, laser granulometry, N2 physisorption, infrared spectroscopy, SEM-EDS and evaluation of the cation exchange capacity, special attention was paid to the influence on the lead adsorption of variables such as adsorbent dosage, pH, contact time with the adsorbate and initial concentration of lead. Considering the cheap and abundant character of the raw materials, their easy processing (no additives were required for their extrusion) and the time and energy save due to no need for further modification through chemical/thermal activation, the obtained results (with retention over 90% for 30 ppm of lead) demonstrated the potential of the proposed design as low cost solution that may be competitive versus other technologies for water depollution, especially in developing regions.

Adsorption and Biomass: Current Interconnections and Future Challenges

The present study focuses on investigating the interconnections between adsorption technology and biomass energy production processes. A critical review on the different roles and perspectives of adsorption in these processes and on the potential of biochar as a solid bio-sorbent is investigated. Adsorption plays a role in CO2 capture as a purification final step and can be viable for capture at low to medium scale. Promising materials and processes are proposed in the literature. Biochar produced from biomass pyrolysis shows properties comparable with commercialized adsorbents. Adsorption in biomass associated with carbon capture and storage (Bio-CCS) is expected to grow if new adsorbents and processes are performant at larger scale. New biomass-based processes involving adsorption can be developed; methanation coupled with methanization is one of them. Biochar is technologically ready for water depollution and soil amendment but further work is needed for CO2 capture applications. These challenges will necessitate adapted policies and R&D to decrease the production costs. Industrial exploitation of biomass necessitates interdisciplinary work.

Photocatalytic degradation of organic pollutant with polypyrrole nanostructures under UV and visible light

Conjugated polymer nanostructures (CPNs) emerge as a new class of photocatalysts for organic pollutant degradation under UV and visible light. Polyprrole (PPy), as a conjugated polymer, exhibits a wide range of applications. We present here the first demonstration of employing pure PPy nanostructures as a very efficient photocatalyst for water depollution. PPy nanostructures were synthesized in hexagonal mesophases (used as soft templates) by chemical polymerization (PPy-NS-c), obtained by radiolysis (PPy-NS-γ), and synthesized without any template via chemical method (PPy-bulk) as bulk. The different PPy samples were characterized by SEM, TEM, FTIR and UV–vis absorption spectroscopy. The photocatalytic activity of both PPy nanostructures (PPy-NS-c and PPy-NS- γ), which remain very stable after several cycles, was evaluated for the degradation of organic pollutant in aqueous solution (phenol and methyl orange were taken as a model pollutant). PPy nanostructures show high photocatalytic activity under both UV and visible light while bulk PPy (PPy-bulk) has no appreciable activity. PPy-NS-c present the highest activity for photodegradation of phenol under UV light, while PPy-NS-γ exhibit the best photocatalytic activity under visible light. We demonstrate here that the nanostructuration of these polymers is an important factor for their application in photocatalysis.

Biodiversity of urban soils for sustainable cities

The last century was marked by a high demographic revolution and the fast development of urban environments. Now, more than 50% of the world’s 7.5 billion humans live in cities. This change has often induced the degradation of environmental quality in urban areas. As a consequence, management policies are now fostering the ‘return of nature’ in cities, which, in turn, is requiring a better understanding of the ecology of urban environments. In particular, there is a need for a better knowledge on soil management because soils provide many functions in cities such as urban agriculture. Optimizing the diversity of soil-living organisms is essential to many environmental functions such as water depollution, biochemical cycles, fertility and carbon storage. However, few studies on the biological quality of urban soils have been performed so far. This article reviews actual knowledge on soil biological quality for urban management. The definition of urban soils is discussed, and we present services provided by soils. We also review modern methods and techniques to assess the biological quality of urban soils. Last, we suggest communication means to improve the consideration of soil quality in urban planning policies aimed at sustainable cities.

Theoretical study of the azo dyes dissociation by advanced oxidation using Fukui indices. DFT calculations

Abstract This work focuses on the study of the degradation to four acid dyes by advanced oxidation; the dyes used are called blue acid 113, 114, 118 and 120. The goal of this study is the determination of the most reactive sites at the levels of the dyes studied, in order to understand the mechanisms of degradation of these dyes in the field of water depollution. The study was carried out theoretically by ab initio methods. The corresponding results were calculated by CAM–B3LYP functional combined with the 6–31++G(d, p) basis set. The calculated parameters are the local Fukui indices for radical attacks, hardnesses, dipole moments, solvation Gibbs free enthalpy ΔGsolv, wavelengths of the maximum absorption and oscillator Strengths. The results showed a good agreement between the mechanisms proposed experimentally and the mechanisms calculated theoretically. Hence, the confirmations of these mechanisms were obtained by local Fukui indices. The latter’s revealed larger values for the nitrogen atoms constituting the four dyes, which confirm that these sites are the most reactive by radical attacks. This study is dedicated for advanced oxidation applications.

Water depollution using metal-organic frameworks-catalyzed advanced oxidation processes: A review.

This paper presents a review on the environmental applications of metal-organic frameworks (MOFs), which are inorganic-organic hybrid highly porous crystalline materials, prepared from metal ion/clusters and multidentate organic ligands. The emphases are made on the enhancement of the performance of advanced oxidation processes (AOPs) (photocatalysis, Fenton reaction methods, and sulfate radical (SO4-)-mediated oxidations) using MOFs materials. MOFs act as adsorption and light absorbers, leading to superior performance of photocatalytic processes. More recent examples of photocatalytic degradation of dyes are presented. Additionally, it is commonly shown that Fe-based MOFs exhibited excellent catalytic performance on the Fenton-based and SO4•--mediated oxidations of organic pollutants (e.g., dyes, phenol and pharmaceuticals). The significantly enhanced generation of reactive species such as OH and/or SO4- by both homogeneous and heterogeneous catalysis was proposed as the possible mechanism for water depollution. Based on the existing literature, the challenge and future perspectives in MOF-based AOPs are addressed.