BACKGROUND: High water consumption and the toxic pollutants found in industrial wastewater are key challenges in achieving a more sustainable development. In this sense, it is crucial to develop sustainable ways to reduce the organic pollutants found in wastewater and to promote its reuse. RESULTS: In this study, a simple, low-cost, and environmentally friendly path for dairy wastewater decontamination through photocatalysis using rod-shaped alpha-Fe2O3/TiO2 type II heterojunctions is reported. The photoreaction of the model solution was evaluated under UVA-visible irradiation with different amounts of alpha-Fe2O3 over TiO2, lactose as pollutant concentrations, Cl- and SO42- anions effects, and oxidant ambient showing up to 42% lactose degradation without the addition of oxidant ambient. Optimized parameters (1.0%wt alpha-Fe2O3/TiO2, [catalyst] = 0.5 g L-1, [lactose] = 0.7 g L-1, [H2O2] = 10 mM, [O-2] = constant) were used on dairy wastewater, which showed a 63% total organic carbon reduction and a 56% chemical oxygen demand reduction. The composite was easily recovered by decantation with a turbidity reduction of similar to 99%. The photocatalyst reusability was assessed over three successive uses and it maintained its activity with a loss of only 10%. CONCLUSION: This study offers a promising approach for the development of innovative sustainable nanotechnology to efficiently degrade organic pollutants commonly found in dairy wastewater and improve its quality within a shorter timeframe. Our approach could contribute to the development of efficient and cost-effective complementary technologies for the Sequencing Batch Reactor in the treatment of dairy wastewater, thus contributing to the sustainability of the dairy industry. (c) 2024 Society of Chemical Industry (SCI).

The photocatalytic conversion in aqueous media of phenol and guaiacol as a lignin model compound using Nb2O5 with different crystal phases was studied. Nb2O5 particles were synthesized using hydrothermal methods, where it was observed that changes in the solvent control their morphology and crystal phase. Different photocatalytic behavior of Nb2O5 was observed with the selected model compounds, indicating that its selection directly impacts the resulting conversion and selectivity rates as well as the reaction pathway, highlighting the relevance of model molecule selection. Photocatalytic conversion of phenol showed conversion rate (C%) up to 25 % after 2 h irradiation and high selectivity (S%) to pyrogallol (up to 50 %). Orthorhombic Nb2O5 spheres favored conversion through free hydroxyl radicals while monoclinic rods did not convert phenol. Guaiacol photocatalytic oxidation showed high conversion rate but lower selectivity. Orthorhombic and monoclinic Nb2O5 favored the formation of resorcinol with S % ~0.43 % (C % ~33 %) and ~13 % (C % ~27 %) respectively. The mixture of both phases enhanced the guaiacol conversion rate to ~55 % with ~17 % of selectivity to salicylaldehyde. The use of radical scavengers provided information to elucidate the reaction pathway for these model compounds, showing that different reaction pathways may be obtained for the same photocatalyst if the model compound is changed.

The photocatalyst response is related to experimental conditions that improve effectiveness in removing contaminants. A parameter analysis of alpha Fe2O3-rutile and water contaminated with methylene blue (MB) was carried out to obtain initial factors that impact reaction conditions. Moreover, the following factors were tested: the alpha Fe2O3-rutile load, the initial MB concentration, and the initial pH solution. These one-factor-at-a-time variations were made to explore the conditions of each variable with the other two fixed. Above all, a significant change was identified in the initial discoloration rate from 5.2 to 35.56 10-9 mol g-1 s-1, with 34 and 91 % removal effectiveness, respectively. These results were achieved with an alpha Fe2O3-rutile load of 1.0 g L-1, an initial MB concentration of 8.0 10-6 mol L-1, and a pH of 8.8, after 540 min of irradiation. This high discoloration effectiveness with alpha Fe2O3-rutile had not been previously reported. The parameter that most influenced the photocatalytic activity was the initial pH solution due to the interaction of the point of zero charge of alpha Fe2O3-rutile and the contaminated water; the pH of the solution exceeds the isoelectric point, it causes electrostatic forces and hydrogen bonds with MB to increase its effectiveness. The combination of alpha Fe2O3-rutile and the removal of methylene blue in water improves adsorption on the surface of the alpha Fe2O3-rutile, providing the highest discoloration rate.

Biomass is a naturally abundant, sustainable, and clean resource, which has the potential to replace fossil feedstock for sustainable production of high add-value chemicals. However, an efficient conversion process is still difficult to achieve due to the difficult reaction conditions. In this study as a novel and versatile concept, we introduced the use of beta-cyclodextrin (beta-CD) macromolecule to enhance the photocatalytic behavior of a alpha-Fe2O3/TiO2 heterojunction. The selective conversion of guaiacol was evaluated using 0.2, 1.0, and 2.0 molar ratios of beta-CD anchored on 0.7 wt % alpha-Fe2O3/TiO2 under mild reaction conditions. 1.0 molar ratio of beta-CD promoted photo-oxidation of guaiacol to mainly produce p-benzoquinone with similar to 68% selectivity at similar to 10% conversion. To understand this effect, Electron Paramagnetic Resonance Spectroscopy (EPR) in operando mode and Diffuse Reflectance Spectroscopy (DRS) experiments were performed. The results showed that the 1.0 molar ratio of beta-CD decreases the bandgap from 3.06 to 2.76 eV and controls the center dot OH radical concentration due to the formation of a covalent bond between beta-CD and semiconductors. The improved guaiacol adsorption capacity on the photocatalyst resulted in the enhancement of the photochemical activity and selectivity. Additionally, a possible pathway of guaiacol transformation was proposed through the oxidation intermediates. Furthermore, the photocatalyst beta-CD/alpha-Fe2O3/TiO2 can be recycled efficiently and reused three times, without loss in reactivity.

The insight into the mechanism of the unprecedented formation of pure anatase TiO2 from the macromolecular (Chitosan)•(TiOSO4)n precursor has been investigated using micro Raman spectroscopy, Scanning Electron Microscopy (SEM) and thermogravimetric/differential thermal analysis (TGA/DTA). The formation of a graphitic film was observed upon annealing of the macromolecular precursor, reaching a maximum at about 500 °C due to decomposition of the polymeric chain of the Chitosan and (PS-co-4-PVP) polymers. The proposed mechanism is the nucleation and growth of TiO2 nanoparticles over this graphitic substrate. SEM and Raman measurements confirm the formation of TiO2 anatase around 400 °C. The observation of an exothermic peak around 260 °C in the TGA/DTA measurements confirms the decomposition of carbon chains to form graphite. Another exothermic peak around 560 °C corresponds to the loss of additional carbonaceous residues.

The sorption behavior of 2,4-dichlorophenoxyacetic acid (2,4-D) in the abundant agricultural volcanic ash-derived soils (VADS) is not well understood despite being widely used throughout the world, causing effects to the environment and human health. The environmental behavior and risk assessment of groundwater pollution by pesticides can be evaluated through kinetic models. This study evaluated the sorption kinetics and 2,4-D sorption–desorption in ten VADS through batch sorption experiments. Differences in the sorption extent for the fast and slow phases was observed through the IPD model where 2,4-D sorption kinetics was controlled by external mass transfer and intra organic matter diffusion in Andisols (C1 ≠ 0). We confirmed from the spectroscopic analysis that the carboxylate group directly drives the interaction of 2,4-D on Andisol soil. The MLR model showed that IEP, FeDCB, and pH×Silt are important soil descriptors in the 2,4-D sorption in VADS. The Freundlich model accurately represented sorption equilibrium data in all cases (Kf values between 1.1 and 24.1 µg1−1/n mL1/ng−1) with comparatively higher sorption capacity on Andisols, where the highest hysteresis was observed in soils that presented the highest and lowest OC content (H close to 0).

Valorization of lignin into high valuable chemical is a critical challenge. Its availability is a key factor for the development of viable lignocellulosic processes to replace fossil derived compounds. In this work, new insights on the high photocatalytic conversion of guaiacol (82%) as a lignin model compound was achieved, also, high selectivity to p-benzoquinone (59%), catechol (27%), and pyrogallol (6%) was obtained using metal-free pyrolyzed g-C3N4 under visible light irradiation. To highlight the new insights, experimental parameters were modified to control the reaction mechanism to increase selectivity and photo-conversion. g-C3N4 photocatalyst was synthesized through urea calcination at 550 degrees C and the photocatalytic performance was assessed in terms of pyrolysis time, where higher time resulted in better photocatalytic activity. This effect was attributed to smaller structures and therefore better quantum confinement of the charges. The oxidation was promoted by OH radicals, which were detected through EPR operando mode and the addition of radical scavengers. A reaction pathway was proposed, in which the OH attacks guaiacol through a methoxy group. The photocatalytic reaction can be tuned using external oxidant agents such as O-2 and/or H2O2 to promote certain radical formation, enhancing conversion rates and promoting selectivity for a specific product, where yield shifting from p-benzoquinone to pyrogallol was experimentally observed.

Three amphiphilic carbon nanotube-supported Ni catalysts have been prepared and tested regarding their emulsifying properties for the hydrogenation of furfural. The solid catalysts and emulsions were systematically characterized by different high-resolution techniques. The catalytic hydrogenation of furfural was evaluated in a mixture of two immiscible solvents under mild conditions. The wettability of the catalysts was tuned by adjusting the severity of the acid treatments during the catalyst's synthesis. It was found that the catalysts wettability played a crucial role in enhancing the catalytic activity. The lowest furfural conversion observed over Ni/CNTox(2) and Ni/CNTp were attributed to the missing possibility to form stable emulsion droplets due to their either extreme hydrophilic or hydrophobic character, respectively. In contrast, the highest catalytic activity verified for Ni/CNTox(1) catalyst was traced back to an improved dispersion of the nickel nanoparticles as well as the possible formation of stable emulsion droplets due to its amphiphilic character. All catalysts were selective towards cyclopentanone. However, the highest yield of cyclopentanone was found over the Ni/CNTox(1) catalyst, which migrated towards the organic phase after its formation. This result highlights the simultaneous reaction and separation of key reaction products in emulsion, which greatly simplifies the isolation stages of target products.

Complexity is a concept that is being considered in chemistry as it has shown potential to reveal interesting phenomena. Thus, it is possible to study chemical phenomena in a new approach called systems chemistry. The systems chemistry has an organization and function, which are regulated by the interactions among its components. At the simplest level, noncovalent interactions between molecules can lead to the emergence of large structures. Consequently, it is possible to go from the molecular to the supramolecular systems chemistry, which aims to develop chemical systems highly complex through intra- and intermolecular forces. Proper use of the interactions previously mentioned allow a glimpse of supramolecular system chemistry in many tasks such as structural properties reflecting certain behaviors in the chemistry of materials, for example, electrical and optical, processes of molecular recognition and among others. In the last time, within this area, inorganic supramolecular systems chemistry has been developed. Those systems have a structural orientation which is defined by certain forces that predominate in the associations among molecules. It is possible to recognize these forces as hydrogen bonding, pi-pi stacking, halogen bonding, electrostatic, hydrophobic, charge transfer, metal coordination, and metallophilic interactions. The presence of these forces in supramolecular system yields certain properties such as light absorption and luminescence. The quantum theoretical modeling plays an important role in the designing of the supramolecular system. The goal is to apply supramolecular principles in order to understand the associated forces in many inorganic molecules that include heavy metals for instance gold, platinum, and mercury. Relevant systems will be studied in detail, considering functional aspects such as enhanced coordination of functionalized molecular self-assembly, electronic and optoelectronic properties.

•The intrinsic properties of rutile were modified through a high energy grinding.•Photocatalysis is controlled by the physical-chemical characteristics of rutile.•The increment of active sites allowed high photoactivity despite the large band gap.

1. Facultad de Química, Centro de Investigación en Nanotecnología y Materiales Avanzados 6 CIEN-UC, Pontificia Universidad Católica de Chile, Vicuña Mackenna 4860, Macul, Santiago 7 de Chile, Chile. 8 2. Instituto de Ciencia de Materiales de Aragón, ICMA, CSIC-Universidad de Zaragoza, María de 9 Luna 3, 50018 – Zaragoza, Spain. 10 3. Departamento de Química, Facultad de Ciencias Básicas, Universidad Metropolitana de 11 Ciencias de la Educación, Santiago, Chile. 12 13

Liquid-phase hydrodeoxygenation of phenol over silica-supported MoOx-ReOx catalysts was investigated at 300 degrees C and 5 MPa of H-2. Mixed-oxides catalysts with similar surface metal density (2.3 atoms of metal per nm(2) of SiO2) but different relative Mo and Re loadings were prepared by incipient wetness impregnation. The catalysts were characterized by N-2 adsorption, temperature programmed reduction (TPR), X-ray photoelectron spectroscopy (XPS), electron paramagnetic resonance (EPR), ultraviolet visible diffuse reflectance (UV-vis-DR) spectroscopy, X-ray diffraction (XRD) and temperature programmed desorption of NH3 (TPD-NH3). All the catalysts were highly active and selective towards deoxygenated products. However, MoOx/SiO2 was the most selective towards cyclohexane formation. Higher amount of benzene was produced with the Re-containing catalysts than it was over the MoOx/SiO2 catalyst, indicating that ReOx favored direct deoxygenation over hydrogenation of the aromatic ring. The catalyst containing equimolar amounts of MoOx and ReOx exhibited the highest yield of benzene. This result can be attributed to a synergistic effect that arises from electronic interaction between rhenium and molybdenum oxides which favors the formation of new oxygen vacancy sites. The study reveals that benzene selectivity is mainly influenced by ReOx sites and the activity can be tuned by a balance of MoOx and ReOx sites.

In an effort to discover new inorganic UV absorbers, titania included into silica was prepared using a solvent-less solid state method involving the pyrolysis of the as prepared precursor Chitosan·(TiOSO4)/SiO2, as an alternative and versatile way to using these compounds for practical applications. The new TiO2/SiO2 composite was characterized by PXRD, SEM–EDS, TEM and UV–Vis absorption analysis. The SEM–EDS mapping images show a uniform distribution of TiO2 into the silica matrix. The optical properties of the composite have shown an interesting result related to high absorption of UVB rays and an improved absorption of UVA rays than pure TiO2. Efficient suppression of photocatalytic behavior of TiO2, when is incorporated into silica, was evidenced from 85 to 31%, suggesting it material as alternative inorganic UV absorber to remains the properties of the methylene blue dye. These results reveal their potential use in practical textile industry and UV protection agent to avoid human damage.

We studied the oxidation reactions of thiocyanate and L-cysteine on iron phthalocyanine (FePc) coupled via a bridging ligand of the 4-mercatopyridine (4MP) type to a gold cluster (Au26), aiming to simulate a modified gold electrode. Theoretical models have been used based on the framework of density functional theory. Several mechanistic pathways are explored for the study of these reactions, finding that the most favorable mechanism involves an electron transfer process as the rate-determining step. Along the process, the ability of the gold cluster to act as an electron acceptor facilitating the reactions was detected. In addition, the proposed models presented a correlation between the energy obtained for the rate-determining step of the reaction and the experimental oxidation potentials of the thiocyanate and L-cysteine.

A controlled physical method without any solvent was used to grow Ag nanoparticles on TiO2 by use of mercaptoacetic acid as a bifunctional surface modifier. The fabricated Ag-TiO2 tight heterojunction was proposed as an innovative photocatalytic material. The particle size, chemical nature, morphology, and chemical bonding between mercaptoacetic acid, Ag, and TiO2 were characterized by UV-vis absorption spectroscopy, powder X-ray diffraction, Raman spectroscopy, transmission electron microscopy, and scanning electron microscopy. The photocatalytic activity of TiO2 combined with the excellent electron acceptor abilities and visible light absorption of small spherical Ag nanoparticles resulted in efficient photoinduced degradation of a cationic organic pollutant (methylene blue) under UV-vis light. The nanocatalyst material obtained with a sputter time of 30 s under simulated sunlight results in almost complete degradation (97%) of methylene blue after 120 min. The particle size, tight attachment to TiO2, and distribution of Ag nanoparticles were controlled for the first time through a physical method by use of controlled chemical bonding to bifunctional surface modifiers and an appropriate sputter deposition time.

Learning the key concepts of chemical kinetics is a challenge for higher education students. These difficulties are due, among other things, to the fact that traditional teaching does not consider the findings of research on students’ learning in this particular domain of chemistry. In this commentary, we propose research-based criteria for the selection of experiments that respond to the learning difficulties in chemical kinetics that have been widely reported in recent years. Additionally, we discuss a teaching strategy that may be appropriate to favor the evolution of students’ intuitive conceptions by evaluating their ideas and those of their peers in the analysis of scientific evidence.

A solid-state phase control of TiO2 by the use of different macromolecular complex precursors is reported for the first time. During the formation of TiO2 nanoparticles, chitosan and poly(styrene-co-4-vinylpyridine) polymers can act as solid-state template producing areas after carbonization, where the TiO2 nucleates. It seems that the location of metal centers through the polymeric chain (i.e., the distance between the metal centers) strongly influences the morphology and particle size of the photocatalyst. To demonstrate the application value of our different TiO2 structures, the photocatalytic behavior was explored. The efficient photocatalytic decoloration of methylene blue on different polymorphic forms of nanostructured TiO2 is confirmed. The best photocatalyst achieved a 98% discoloration rate in only 25 min when the pH of the solution was 9.5, improving the efficiency of the standard photocatalyst Degussa P25 without the addition of other phases or dopants. The novelty of the present work is that, by means of an appropriate synthesis, the three main factors (morphology, size, and crystalline phase) that allow modulating the photocatalytic response of titania material can be tuned simultaneously. This control has allowed an advance in the properties of the material, managing to increase the photoresponse in a short time.