Three distinct sol-gel synthesis methodologies were employed to fabricate niobium catalysts supported on stainless steel meshes via the dip-coating technique, with the objective of their utilization ...in layered configurations for water purification applications. The structured catalysts were subjected to calcination at three varying temperatures: no calcination, calcination at 823 K, and calcination at 1173 K. Ibuprofen, selected as the model pollutant due to its emerging contaminant profile, was utilized for evaluation. Scanning electron microscopy (SEM) and energy dispersive X-ray spectroscopy (EDS) images, in conjunction with adhesion assessments, elucidated that thermally treated catalysts exhibited nearly 80% retention of Nb
2
O
5
nanoparticles adhered uniformly to the support surface. In batch reactor experiments, the catalyst derived from the NbCl
5
precursor and polyacrylonitrile (PAN) exhibited the most promising performance, achieving a 90% degradation of the contaminant within a 120 min timeframe. This catalyst, exhibiting superior efficacy, was subsequently employed in tests utilizing photocatalytic bench reactors, where it demonstrated analogous performance to that observed in the batch reactor setup. Upon upscaling to a high-capacity photocatalytic prototype, the degradation efficiency was sustained above that observed in photolytic testing, even after four utilization cycles.
Brazil, the largest global sugar cane producer, utilizes approximately 10 million hectares for cultivation. However, the increased use of agrochemicals in this industry raises concerns about ...environmental and human health impacts. Inclusively, ametryn (AMT), a pesticide intensively used in sugar cane plantations, has been detected in several water matrices at concerning levels, which evidences the urgent need for the development of technologies capable of removing this pesticide from the environment. This study investigated the removal efficiency of AMT from aquatic environments via oxidation promoted by persulfate (PS) activation mediated by carbon-based materials, such as graphene, carbon nanotubes, and activated carbon. Granular activated carbon (GAC) emerged as the most suitable material due to its clear catalytic role. A central composite design was used to evaluate and optimize the factors influencing AMT degradation and mineralization, revealing that the initial PS concentration and GAC dosage strongly impact the degradation rate and organic carbon removal in different directions. GAC was submitted to surface functionalization with N- and O-precursors to investigate how this impacts PS activation, and positive enhancements were noted with the latter, with a mineralization degree 9% superior. Experiments with real water matrices evidence the impact of other water constituents on the degradation rate of the target pollutant (k′ 300), which was reduced by half when performed in groundwater. Notwithstanding, the system still demonstrated a consistent capacity to remove organic content, ranging from 60 to 50% TOCremoval, regardless of the water matrix, indicating that the system might be effective in real contamination scenarios. This research highlights the potential of GAC and its modified version for remediation of AMT-contaminated water remediation.
Different lanthanide (Ln)-doped cerium oxides (Ce0.5Ln0.5O1.75, where Ln: Gd, La, Pr, Nd, Sm) were loaded with Cu (20 wt. %) and used as catalysts for the oxidation of ethyl acetate (EtOAc), a common ...volatile organic compound (VOC). For comparison, both Cu-free (Ce-Ln) and supported Cu (Cu/Ce-Ln) samples were characterized by N₂ adsorption at -196 °C, scanning/transmission electron microscopy, energy-dispersive X-ray spectroscopy, X-ray diffraction, X-ray photoelectron spectroscopy and temperature programmed reduction in H₂. The following activity sequence, in terms of EtOAc conversion, was found for bare supports: CeO₂ ≈ Ce0.5Pr0.5O1.75 > Ce0.5Sm0.5O1.75 > Ce0.5Gd0.5O1.75 > Ce0.5Nd0.5O1.75 > Ce0.5La0.5O1.75. Cu addition improved the catalytic performance, without affecting the activity order. The best catalytic performance was obtained for Cu/CeO₂ and Cu/Ce0.5Pr0.5O1.75 samples, both achieving complete EtOAc conversion below ca. 290 °C. A strong correlation was revealed between the catalytic performance and the redox properties of the samples, in terms of reducibility and lattice oxygen availability. Νo particular correlation between the VOC oxidation performance and textural characteristics was found. The obtained results can be explained in terms of a Mars-van Krevelen type redox mechanism involving the participation of weakly bound (easily reduced) lattice oxygen and its consequent replenishment by gas phase oxygen.
Five different biomass wastes—orange peel, coffee grounds, cork, almond shell, and peanut shell—were transformed into biochars (BCs) or activated carbons (ACs) to serve as adsorbents and/or ozone ...catalysts for the removal of recalcitrant water treatment products. Oxalic acid (OXL) was used as a model pollutant due to its known refractory character towards ozone. The obtained materials were characterized by different techniques, namely thermogravimetric analysis, specific surface area measurement by nitrogen adsorption, and elemental analysis. In adsorption experiments, BCs generally outperformed ACs, except for cork-derived materials. Orange peel BC revealed the highest adsorption capacity (Qe = 40 mg g−1), while almond shell BC showed the best cost–benefit ratio at €0.0096 per mg of OXL adsorbed. In terms of catalytic ozonation, only ACs made from cork and coffee grounds presented significant catalytic activity, achieving pollutant removal rates of 72 and 64%, respectively. Among these materials, ACs made from coffee grounds reveal the best cost/benefit ratio with €0.02 per mg of OXL degraded. Despite the cost analysis showing that these materials are not the cheapest options, other aspects rather than the price alone must be considered in the decision-making process for implementation. This study highlights the promising role of biomass wastes as precursors for efficient and eco-friendly water treatment processes, whether as adsorbents following ozone water treatment or as catalysts in the ozonation reaction itself.
This study describes the synthesis of Nb2O5 by three sol-gel methods to be used as a catalyst in photocatalysis, catalytic ozonation and the synergistic effects of the two processes, photocatalytic ...ozonation in bath reactions for the degradation of ibuprofen and its degradation products, 4- Isobutylacetophenone and oxalic acid. The catalysts were prepared in three temperature ranges: non-calcined, calcined at 873 K and 1173 K, and were characterized using different techniques. The results demonstrate that the catalyst synthesized through Sol-gel Method 3 and heat-treated at 873 K achieved the highest pollutant removal in photocatalytic tests (92% with 95% TOC reduction) over 300 min of reaction, and in the catalytic ozonation tests (100% with 62% TOC reduction) over 30 min of reaction, due to the combination of the properties presented in the characterization analyzes. Thus, this catalyst was employed in photocatalytic ozonation reactions and demonstrated the capability to degrade 100% of ibuprofen in 12 min without 4-IBAP formation, resulting in a 98% reduction in TOC over 30 min of reaction. In addition, the photostability outcomes of this catalyst demonstrated no significant reduction in catalytic activity during the photocatalytic and catalytic ozonation processes and comparable results to P25. The toxicity tests validated the TOC results, showing an 8% effect vs. 90% of ibuprofen starting solution, and 43% effect vs. 95% of 4-IBAP starting solution.
Display omitted
•Combatting Organic Pollutants: Ibuprofen on the Rise.•Three Nb2O5 Sol-Gel Catalyst Methods Explored.•Photocatalytic and Ozonation Tests for Water Purification.•Nb2O5 Sol-Gel Method 3 Similar to P25.•High Ibuprofen Degradation via Photocatalytic Ozonation.
Multiwalled carbon nanotubes (MWCNTs) are known to have great potential to be used as catalysts in the ozonation of organic pollutants in water. However, solutions are required toward their practical ...application to overcome difficulties with the handling of nanosized powders. One such alternative is their coating on macrostructured ceramic supports. The majority of instances of such applications are based on the in situ formation of a nanocarbon layer by chemical vapor deposition. With recent advances in the modification of MWCNTs by mechanical methodologies showing that these can enhance their catalytic activity, there is an interest in the coating of ceramic macrostructures with a premodified MWCNTs because mechanical methods are not applicable to in situ grown materials. The coating of a MWCNTs using a conventional dip-coating technique would allow for premodification of the carbon by mechanical means. However, several obstacles in the formation of the slurry and nanostructured layers exist because of the behavior of the MWCNTs in suspension. In this work, the textural and morphological modification of MWCNTs by ball milling and subsequent interaction with different organic binders and surfactants in slurries was investigated. The main characteristics influencing the slurry stability and its use in the dip-coating of cordierite macrostructures were identified. Different modes of nanostructured layer formation were observed depending on the particle size distribution of the slurry, which is influenced by the surface chemistry and morphology of the MWCNTs. A correlation between the nanostructured layer homogeneity and adhesion and the slurry particle size distribution was established. This understanding was applied to form nanostructured layers with a pretreated nitrogen-containing MWCNTs. The material’s basic character resulted in larger slurry particle sizes and consequently poorly adhered coatings. An approach using a premixed MWCNTs with a nitrogen precursor was shown to be able to produce nanostructured coatings with a nitrogen-doped MWCNTs and good adherence. The resulting nanostructured layers of MWCNTs were found to be catalytically active in the ozonation of a model organic pollutant (oxalic acid).
A large number of methodologies for fabrication of 1D carbon nanomaterials have been developed in the past few years and are extensively described in the literature. However, for many applications, ...and in particular in catalysis, a translation of the materials to a macro-structured form is often required towards their use in practical operation conditions. This review intends to describe the available methods currently used for fabrication of such macro-structures, either already applied or with potential for application in the fabrication of macro-structured catalysts containing 1D carbon nanomaterials. A review of the processing methods used in the fabrication of macrostructures containing 1D sp2 hybridized carbon nanomaterials is presented. The carbon nanomaterials here discussed include single- and multi-walled carbon nanotubes, and several types of carbon nanofibers (fishbone, platelet, stacked cup, etc.). As the processing methods used in the fabrication of the macrostructures are generally very similar for any of the carbon nanotubes or nanofibers due to their similar chemical nature (constituted by stacked ordered graphene planes), the review aggregates all under the carbon nanofiber (CNF) moniker. The review is divided into methods where the CNFs are synthesized already in the form of a macrostructure (in situ methods) or where the CNFs are previously synthesized and then further processed into the desired macrostructures (ex situ methods). We highlight in particular the advantages of each approach, including a (non-exhaustive) description of methods commonly described for in situ and ex situ preparation of the catalytic macro-structures. The review proposes methods useful in the preparation of catalytic structures, and thus a number of techniques are left out which are used in the fabrication of CNF-containing structures with no exposure of the carbon materials to reactants due to, for example, complete coverage of the CNF. During the description of the methodologies, several different macrostructures are described. A brief overview of the potential applications of such structures in catalysis is also offered herein, together with a short description of the catalytic potential of CNFs in general.
Display omitted
•macro-structured ozonation catalysts were prepared using ball-milled MWCNT.•the coating procedure hindered the catalytic performance of the ball-milled MWCNT.•the packing of the ...MWCNT upon coating was found to affect the catalysts’ performance.•the catalysts still compared favourably against a reference MWCNT coated sample.•surface functionalization of MWCNT improved the stability of the catalysts.
A series of macro-structured catalysts consisting of nanostructured layers of mechanically processed multiwalled carbon nanotubes (MWCNT) coated onto cordierite monoliths were prepared using a novel methodology and assessed as catalysts in the ozonation of a model organic pollutant. The often used chemical vapor deposition method for formation of nanostructured layers of carbon materials is, by nature, incompatible with ball-milling or other methods for mechanical or mechano-chemical modification of MWCNT. The preparation method here described was designed to translate the positive effect observed in the performance of ball-milled MWCNT as ozonation catalysts when compared with unmodified MWCNT to macro-structured catalytic systems. The performance of such macro-structured catalysts in the ozonation of organic pollutants is reported and analyzed for the first time. The effect of the preparation methodology, which includes physical functionalization of the MWCNT with a non-ionic surfactant (Triton X-100®), in the performance of the powder catalysts was evaluated. It was found that, for the coated nanostructured layers, the decrease in the expected activity is related to the packing of the materials. Nevertheless, the catalytic nanostructured coated layers were found to compare favorably with a reference sample. Thus, the beneficial effect of ball-milling MWCNT is still retained upon coating, even with a decrease in the intrinsic activity of the powder material. The increase in MWCNT mass in the coated samples introduces diffusion limitations, suggesting that creating a macroporous system in the MWCNT layers might be desirable. The introduction of oxygen-containing surface functionalities improved the long-term stability of the nanostructured catalytic layers.
Catalytic reduction in water is a potential alternative to replace current available techniques, such as adsorption or ion-exchange, for the efficient treatment of perchlorate contaminated waters. ...However, the development of an efficient catalytic system has been hindered by the perchlorate’s very stable tetrahedral structure. This work aims to obtain an efficient catalytic system to degrade perchlorate in contaminated water at natural pH and mild operation conditions by optimizing the design of a supported catalyst. To this end, different metal combinations, using Pt, Pd, and Ru in combination with Re were tested. The most active metallic pairing (Re/Pt) was then used in a systematic study to optimize its composition. An optimal composition that promotes the formation of coordinated Re/Pt species was established. This facilitates the interaction of perchlorate with spilled-over hydrogen, consequently resulting in improved reaction rates above those reported elsewhere. The stability of the catalytic system was demonstrated in reutilization experiments under anoxic atmosphere.
A systematic catalyst development study allows the rational design of a catalytic system to effectively remove perchlorate, a very stable water contaminant, from water.
Display omitted
•Bimetallic Re catalysts were prepared for the reduction of perchlorate in water.•A systematic study identified the most promising noble metal pairing for Re (Re/Pt).•Different metal weight contents were screened and an optimised ratio was found.•Catalytic activity trend was related to hydrogen uptake during pulse chemisorption.•Improved perchlorate removal was related with formation of Re/Pt surface species.
The presence of nitrate in water is presently a common problem across Europe. The catalytic reduction of nitrate has been suggested in the literature as a promising method for its elimination, ...without the drawbacks of the conventional technologies. This process consists in the reduction of nitrate to nitrogen over bimetallic catalysts in the presence of a reducing agent. The main objective of this work was the study of the catalytic reduction of nitrate in water with hydrogen in a systematic way, evaluating several metal catalysts and their composition, preparation conditions and supports, focusing on the use of activated carbon as support, and clarifying some mechanistic aspects. The first goal of this thesis was the evaluation of monometallic and bimetallic catalysts supported on activated carbon for nitrate and nitrite reduction, in order to select the most promising catalytic systems for further developments. It was observed that the monometallic catalysts supported on activated carbon were inactive or practically inactive for nitrate reduction but that they were active for nitrite reduction. The pairs Pd-Cu, Pt-Cu, Rh-Cu and Ir-Cu supported on activated carbon were studied in detail in order to establish their best formulation. It was shown that the efficiency of the catalysts is quite different depending on the copper content. The maximum activity was obtained for an atomic ratio noble metal/copper close to 1, which is indicative that the same amount of noble metal and promoter atoms is the best formulation to obtain a very active catalyst for this reaction. The selectivity to nitrogen increases with the atomic copper content up to 75%. In addition to the type of supported metals, the reduction of nitrate is quite dependent on the preparation conditions (calcination and reduction temperatures). For the Pd-Cu and Pt-Cu bimetallic catalysts, it was observed that the activity decreases with the increase of calcination and reduction temperatures, whereas the effect on the selectivity is not uniform. The formation of alloys during the preparation of the catalysts is prejudicial for catalysts performance. The calcination at 200 ºC and reduction at 100 ºC seem to be the optimal temperatures to prepare the catalysts supported on activated carbon, when both activity and nitrogen selectivity are considered. Physical mixtures of Pd and Cu or Pt and Cu monometallic catalysts perform similarly or even better than the corresponding bimetallic catalysts. This fact indicates that the initial presence of bimetallic sites on the catalysts for the reduction of nitrate is not mandatory; it is sufficient that both metals are present in the reaction system. Nevertheless, the noble metal must be already supported and copper does not need to be in the metallic form. Based on these observations, a reaction mechanism considering that the nitrate reduction can occur in the presence of a bimetallic catalyst or a physical mixture of monometallic catalysts was proposed. The surface chemistry of the support plays an important role in the catalyst activity and selectivity, being its influence more pronounced when Pt-Cu catalysts are used. Comparing the different carbon supports tested, basic samples and carbon nanotubes were the best, whereas carbon xerogels were the worst supports for this reaction. Carbon nanotubes demonstrate to be a good support for this reaction. The results obtained show that the reduction of nitrate is quite different depending on the noble metal, the preparation conditions and the support used, as observed when activated carbon is used as support. Several metals oxides, as well as metal oxides and activated carbon or carbon nanotubes composites, were also assessed as supports for nitrate reduction. It was observed that the support has an important effect on the catalytic performance and in some cases (ceria and titania) is involved in the reaction mechanism. Nevertheless, the supports are not active; the presence of one or two metals is mandatory to reduce nitrate. The results obtained show that titanium dioxide provides high activity for nitrate reduction and that the use of a composite with carbon nanotubes increases significantly the selectivity of the process to nitrogen. The catalysts supported on ceria are very selective to nitrogen and present the particularity of the monometallic to be more active than the bimetallic. Manganese oxides are not suitable supports for this reaction. For all the preparation conditions tested, the Pd-Cu pair is the most selective in the transformation of nitrate into nitrogen. Selectivities to nitrogen as high as 82% and 76% were obtained with the 1%Pd-1%Cu bimetallic catalyst supported on carbon nanotubes and activated carbon, respectively. In some experiments, nitrate conversions near 100% were obtained, but in these cases the allowable ammonium values in drinking water were always exceeded.
PDF
