Improved L-Asparaginase Properties and Reusability by Immobilization onto Functionalized Carbon Xerogels.

Enzyme immobilization can offer a range of significant advantages, including reusability, and increased selectivity, stability, and activity. In this work, a central composite design (CCD) of experiments and response surface methodology (RSM) were used to study, for the first time, the L-asparaginase (ASNase) immobilization onto functionalized carbon xerogels (CXs). The best results were achieved using CXs obtained by hydrothermal oxidation with nitric acid and subsequent heat treatment in a nitrogen flow at 600 °C (CX-OX-600). Under the optimal conditions (81 min of contact time, pH 6.2 and 0.36 g/L of ASNase), an immobilization yield (IY) of 100 % and relative recovered activity (RRA) of 103 % were achieved. The kinetic parameters obtained also indicate a 1.25-fold increase in the affinity of ASNase towards the substrate after immobilization. Moreover, the immobilized enzyme retained 97 % of its initial activity after 6 consecutive reaction cycles. All these outcomes confirm the promising properties of functionalized CXs as support for ASNase, bringing new insights into the development of an efficient and stable immobilization platform for use in the pharmaceutical industry, food industry, and biosensors.

A thiomolybdate cluster for visible-light-driven hydrogen evolution: comparison of homogeneous and heterogeneous approaches.

This study investigates the hydrogen evolution reaction (HER) efficiency of two photosystems incorporating an all-inorganic molecular thiomolybdate [Mo3S13]2- cluster as a HER catalyst. First, we delve into the performance of a homogeneous [Mo3S13]2-/[Ru(bpy)3]2+ (Mo3/Ru) dyad which demonstrates high turnover frequencies (TOFs) and apparent quantum yields (AQYs) at 445 nm approaching the level of 0.5%, yet its performance is marked by pronounced deactivation. In contrast, a heterogeneous approach involves anchoring [Mo3S13]2- onto graphitic carbon nitride (GCN) nanosheets through weak electrostatic association with its triazine/heptazine scaffold. [Mo3S13]2-/GCN (Mo3/GCN) displays effective H2 generation under visible light, with TOF metrics on par with those of its homogeneous analog. Although substantial leaching of [Mo3S13]2- species from the Mo3/GCN surface occurs, the remaining {Mo3}-based centers demonstrate impressive stability, leading to enduring HER performance, starkly distinguishing it from the homogeneous Mo3/Ru photosystem. Photoluminescence (PL) quenching experiments confirm that the performance of Mo3/GCN is not limited by the quality of the inorganic interface, but could be optimized by using higher surface area supports or a higher concentration of [Mo3S13]2- sites. Our findings showcase complexities underlying the evaluation and comparison of photosystems comprising well-defined catalytic centers and pave the way for developing analogous surface-supported (photo)catalysts with broad use in energy applications.

Novel photoelectrochemical 3D-system for water disinfection by deposition of modified carbon nitride on vitreous carbon foam.

Graphitic carbon nitride (GCN) is an optical semiconductor with excellent photoactivity under visible light irradiation. It has been widely applied for organic micropollutant removal from contaminated water, and less investigated for microorganisms' inactivation. The photocatalytic degradation mechanism using GCN is attributed to a series of reactions with reactive oxygen species and photogenerated holes that can be boosted by modifying its physical-chemical structure. This work reports a successful improvement of the overall photocatalytic and electrocatalytic activities of the pristine material by thermal and chemical modification by a copolymerisation synthesis method. The copolymerisation of dicyandiamide as a precursor with barbituric acid strongly reduced photoluminescence due to the enhanced charge separation thus improving the catalyst efficiency under visible light irradiation. The material with 1.6 wt% of barbituric acid showed the best photocatalytic performance and electrochemical properties. This photocatalyst was selected for immobilisation on a conductive carbon foam, which promotes a higher electrochemical active surface area and enhanced mass transfer. This three-dimensional metal-free electrode was employed for the photoelectrochemical inactivation of two different microorganisms, Escherichia coli, and Enterococcus faecalis, obtaining removals below the detection limit after 30 min in simulated faecal-contaminated waters. This photoelectrochemical reactor was also applied to treat polluted river and urban waste waters, and the faecal contamination indicators were vastly reduced to values below the detection limit in 60 min in both cases, showing the wide applicability of this innovative photoelectrode for different types of polluted aqueous matrices.

Photocatalytic Hydrogen Production using Porous 3D Graphene-Based Aerogels Supporting Pt/TiO2 Nanoparticles.

Composites involving reduced graphene oxide (rGO) aerogels supporting Pt/TiO2 nanoparticles were fabricated using a one-pot supercritical CO2 gelling and drying method, followed by mild reduction under a N2 atmosphere. Electron microscopy images and N2 adsorption/desorption isotherms indicate the formation of 3D monolithic aerogels with a meso/macroporous morphology. A comprehensive evaluation of the synthesized photocatalyst was carried out with a focus on the target application: the photocatalytic production of H2 from methanol in aqueous media. The reaction conditions (water/methanol ratio, catalyst concentration), together with the aerogel composition (Pt/TiO2/rGO ratio) and architecture (size of the aerogel pieces), were the factors that varied in optimizing the process. These experimental parameters influenced the diffusion of the reactants/products inside the aerogel, the permeability of the porous structure, and the light-harvesting properties, all determined in this study towards maximizing H2 production. Using methanol as the sacrificial agent, the measured H2 production rate for the optimized system (18,800 µmolH2h-1gNPs-1) was remarkably higher than the values found in the literature for similar Pt/TiO2/rGO catalysts and reaction media (2000-10,000 µmolH2h-1gNPs-1).

Aliivibrio fischeri L-Asparaginase production by engineered Bacillus subtilis: a potential new biopharmaceutical.

L-Asparaginase (L-ASNase) is an enzyme applied in the treatment of lymphoid malignancies. However, an innovative L-ASNase with high yield and lower side effects than the commercially available preparations are still a market requirement. Here, a new-engineered Bacillus subtilis strain was evaluated for Aliivibrio fischeri L-ASNase II production, being the bioprocess development and the enzyme characterization studied. The pBS0E plasmid replicative in Bacillus sp and containing PxylA promoter inducible by xylose and its repressive molecule sequence (XylR) was used for the genetic modification. Initially, cultivations were carried out in orbital shaker, and then the process was scaled up to stirred tank bioreactor (STB). After the bioprocess, the cells were recovered and submitted to ultrasound sonication for cells disruption and intracellular enzyme recovery. The enzymatic extract was characterized to assess its biochemical, kinetic and thermal properties using L-Asparagine and L-Glutamine as substrates. The results indicated the potential enzyme production in STB achieving L-ASNase activity up to 1.539 U mL-1. The enzymatic extract showed an optimum pH of 7.5, high L-Asparagine affinity (Km = 1.2275 mmol L-1) and low L-Glutaminase activity (0.568-0.738 U mL-1). In addition, thermal inactivation was analyzed by two different Kinect models to elucidate inactivation mechanisms, low kinetic thermal inactivation constants for 25 ºC and 37 ºC (0.128 and 0.148 h-1, respectively) indicate an elevated stability. The findings herein show that the produced recombinant L-ASNase has potential to be applied for pharmaceutical purposes.

Immobilization and Characterization of L-Asparaginase over Carbon Xerogels.

L-asparaginase (ASNase) is an aminohydrolase currently used in the pharmaceutical and food industries. Enzyme immobilization is an exciting option for both applications, allowing for a more straightforward recovery and increased stability. High surface area and customizable porosity make carbon xerogels (CXs) promising materials for ASNase immobilization. This work describes the influence of contact time, pH, and ASNase concentration on the immobilization yield (IY) and relative recovered activity (RRA) using the Central Composite Design methodology. The most promising results were obtained using CX with an average pore size of 4 nm (CX-4), reaching IY and RRA of 100%. At the optimal conditions (contact time 49 min, pH 6.73, and [ASNase] 0.26 mg·mL-1), the ASNase-CXs biocomposite was characterized and evaluated in terms of kinetic properties and operational, thermal, and pH stabilities. The immobilized ASNase onto CX-4 retained 71% of its original activity after six continuous reaction cycles, showed good thermal stability at 37 °C (RRA of 91% after 90 min), and was able to adapt to both acidic and alkaline environments. Finally, the results indicated a 3.9-fold increase in the immobilized ASNase affinity for the substrate, confirming the potential of CXs as a support for ASNase and as a cost-effective tool for subsequent use in the therapeutic and food sectors.

Impact of atomic layer deposited TiO2 on the photocatalytic efficiency of TiO2/w-VA-CNT nanocomposite materials.

Titanium oxide (TiO2) has been widely investigated as a photocatalytic material, and the fact that its performance depends on its crystalline structure motivates further research on the relationship between preparation methods and material properties. In this work, TiO2 thin films were grown on non-functionalized wave-like patterned vertically aligned carbon nanotubes (w-VA-CNTs) via the atomic layer deposition (ALD) technique. Grazing incidence X-ray diffraction (GIXRD) analysis revealed that the structure of the TiO2/VA-CNT nanocomposites varied from amorphous to a crystalline phase with increasing deposition temperature, suggesting a "critical deposition temperature" for the anatase crystalline phase formation. On the other hand, scanning transmission electron microscopy (STEM) studies revealed that the non-functionalized carbon nanotubes were conformally and homogeneously coated with TiO2, forming a nanocomposite while preserving the morphology of the nanotubes. X-ray photoelectron spectroscopy (XPS) provided information about the surface chemistry and stoichiometry of TiO2. The photodegradation experiments under ultraviolet (UV) light on a model pollutant (Rhodamine B, RhB) revealed that the nanocomposite comprised of anatase crystalline TiO2 grown at 200 °C (11.2 nm thickness) presented the highest degradation efficiency viz 55% with an illumination time of 240 min. Furthermore, its recyclability was also demonstrated for multiple cycles, showing good recovery and potential for practical applications.

Synthesis of Vitamin B3 through a Heterogeneous Photocatalytic Approach Using Metal-Free Carbon Nitride-Based Catalysts.

Vitamin B3 (nicotinic acid, VB3) was synthesized through the photocatalytic oxidation of 3-pyridinemethanol (3PM) under visible-light-emitting diode (LED) irradiation using metal-free graphitic carbon nitride (GCN) - based materials. A bulk (GCN) material was prepared by a simple thermal treatment using dicyandiamide as the precursor. A post-thermal treatment under static air and nitrogen flow was employed to obtain the GCN-T and GCN-T-N materials, respectively. The conditions adopted during the post-treatment revealed differences in the resulting materials' morphological, electronic, and optical properties. The post-treated photocatalysts revealed an enhanced efficiency in the oxidation of 3PM into VB3, with the GCN-T-N photocatalyst being the best-performing material. The defective surface, reduced crystallinity, and superior photoabsorption of GCN-T-N account for this material's improved performance in the production of VB3. Nevertheless, the presence of nitrogen vacancies in the carbon nitride structure and, consequently, the creation of mid-gap states also accounts to its highly oxidative ability. The immobilization of GCN-T-N in sodium alginate hydrogel was revealed as a promising strategy to produce VB3, avoiding the need for the photocatalyst separation step. Concerning the mechanism of synthesis of VB3 through the photocatalytic oxidation of 3PM, it was possible to identify the presence of 3-pyridinecarboxaldehyde (3PC) as the intermediary product.

Superior operational stability of immobilized L-asparaginase over surface-modified carbon nanotubes.

L-asparaginase (ASNase, EC 3.5.1.1) is an enzyme that catalyzes the L-asparagine hydrolysis into L-aspartic acid and ammonia, being mainly applied in pharmaceutical and food industries. However, some disadvantages are associated with its free form, such as the ASNase short half-life, which may be overcome by enzyme immobilization. In this work, the immobilization of ASNase by adsorption over pristine and modified multi-walled carbon nanotubes (MWCNTs) was investigated, the latter corresponding to functionalized MWCNTs through a hydrothermal oxidation treatment. Different operating conditions, including pH, contact time and ASNase/MWCNT mass ratio, as well as the operational stability of the immobilized ASNase, were evaluated. For comparison purposes, data regarding the ASNase immobilization with pristine MWCNT was detailed. The characterization of the ASNase-MWCNT bioconjugate was addressed using different techniques, namely Transmission Electron Microscopy (TEM), Thermogravimetric Analysis (TGA) and Raman spectroscopy. Functionalized MWCNTs showed promising results, with an immobilization yield and a relative recovered activity of commercial ASNase above 95% under the optimized adsorption conditions (pH 8, 60 min of contact and 1.5 × 10-3 g mL-1 of ASNase). The ASNase-MWCNT bioconjugate also showed improved enzyme operational stability (6 consecutive reaction cycles without activity loss), paving the way for its use in industrial processes.

Light-driven oxygen evolution from water oxidation with immobilised TiO2 engineered for high performance.

Calcination treatments in the range of 500-900 °C of TiO2 synthesised by the sol-gel resulted in materials with variable physicochemical (i.e., optical, specific surface area, crystallite size and crystalline phase) and morphological properties. The photocatalytic performance of the prepared materials was evaluated in the oxygen evolution reaction (OER) following UV-LED irradiation of aqueous solutions containing iron ions as sacrificial electron acceptors. The highest activity for water oxidation was obtained with the photocatalyst thermally treated at 700 °C (TiO2-700). Photocatalysts with larger anatase to rutile ratio of the crystalline phases and higher surface density of oxygen vacancies (defects) displayed the best performance in OER. The oxygen defects at the photocatalyst surface have proven to be responsible for the enhanced photoactivity, acting as important active adsorption sites for water oxidation. Seeking technological application, water oxidation was accomplished by immobilising the photocatalyst with the highest OER rate measured under the established batch conditions (TiO2-700). Experiments operating under continuous mode revealed a remarkable efficiency for oxygen production, exceeding 12% of the apparent quantum efficiency (AQE) at 384 nm (UV-LED system) compared to the batch operation mode.

Advances on Graphyne-Family Members for Superior Photocatalytic Behavior.

Graphyne (GY) and graphdiyne (GDY) have been employed in photocatalysis since 2012, presenting intriguing electronic and optical properties, such as high electron mobility and intrinsic bandgap due to their high π-conjugated structures. Authors are reporting the enhanced photocatalytic efficiency of these carbon allotropes when combined with different metal oxides or other carbon materials. However, the synthesis of graphyne-family members (GFMs) is still very recent, and not much is known about the true potential of these photocatalytic materials. In this review article, the implications of different synthesis routes on the structural features and photocatalytic properties of these materials are elucidated. The application of GFMs in the nicotinamide adenine dinucleotide (NADH) regeneration, hydrogen and oxygen evolution, and carbon dioxide reduction is discussed, as well as in the degradation of pollutants and bacteria inactivation in water and wastewater treatment.

Recent Strategies and Applications for l-Asparaginase Confinement.

l-asparaginase (ASNase, EC 3.5.1.1) is an aminohydrolase enzyme with important uses in the therapeutic/pharmaceutical and food industries. Its main applications are as an anticancer drug, mostly for acute lymphoblastic leukaemia (ALL) treatment, and in acrylamide reduction when starch-rich foods are cooked at temperatures above 100 °C. Its use as a biosensor for asparagine in both industries has also been reported. However, there are certain challenges associated with ASNase applications. Depending on the ASNase source, the major challenges of its pharmaceutical application are the hypersensitivity reactions that it causes in ALL patients and its short half-life and fast plasma clearance in the blood system by native proteases. In addition, ASNase is generally unstable and it is a thermolabile enzyme, which also hinders its application in the food sector. These drawbacks have been overcome by the ASNase confinement in different (nano)materials through distinct techniques, such as physical adsorption, covalent attachment and entrapment. Overall, this review describes the most recent strategies reported for ASNase confinement in numerous (nano)materials, highlighting its improved properties, especially specificity, half-life enhancement and thermal and operational stability improvement, allowing its reuse, increased proteolysis resistance and immunogenicity elimination. The most recent applications of confined ASNase in nanomaterials are reviewed for the first time, simultaneously providing prospects in the described fields of application.

Aqueous solution photocatalytic synthesis of p-anisaldehyde by using graphite-like carbon nitride photocatalysts obtained via the hard-templating route.

Graphite-like carbon nitride (GCN)-based materials were developed via the hard-templating route, using dicyandiamide as the GCN precursor and silica templates. That resulted in urchin-like GCN (GCN-UL), 3D ordered macroporous GCN (GCN-OM) and mesoporous GCN (GCN-MP). The introduction of silica templates during GCN synthesis produced physical defects on its surface, as confirmed by SEM analysis, increasing their specific surface area. A high amount of nitrogen vacancies is present in modified catalysts (revealed by XPS measurements), which can be related to an increase in the reactive sites available to catalyse redox reactions. The textural and morphological modifications induced in GCN an enhanced light absorption capacity and reduced electron/hole recombination rate, contributing to its improved photocatalytic performance. In the photocatalytic conversion of p-anisyl alcohol to p-anisaldehyde in deoxygenated aqueous solutions under UV-LED irradiation, the GCN-UL was the best photocatalyst reaching 60% yield at 64% conversion for p-anisaldehyde production after 240 min of reaction. Under oxygenated conditions (air), the process efficiency was increased to 79% yield at 92% conversion only after 90 min reaction. The GCN-based photocatalyst kept its performance when using visible-LED radiation under air atmosphere. Trapping of photogenerated holes and radicals by selective scavengers showed that under deoxygenated conditions, holes played the primary role in the p-anisaldehyde synthesis. Under oxygenated conditions, the process is governed by the effect of reactive oxygen species, namely superoxide radicals, with a significant contribution from holes.

Development and characterization of a novel l-asparaginase/MWCNT nanobioconjugate.

The enzyme l-asparaginase (ASNase) presents effective antineoplastic properties used for acute lymphoblastic leukemia treatment besides their potential use in the food sector to decrease the acrylamide formation. Considering their applications, the improvement of this enzyme's properties by efficient immobilization techniques is in high demand. Carbon nanotubes are promising enzyme immobilization supports, since these materials have increased surface area and effective capacity for enzyme loading. Accordingly, in this study, multi-walled carbon nanotubes (MWCNTs) were explored as novel supports for ASNase immobilization by a simple adsorption method. The effect of pH and contact time of immobilization, as well as the ASNase to nanoparticles mass ratio, were optimized according to the enzyme immobilization yield and relative recovered activity. The enzyme-MWCNTs bioconjugation was confirmed by thermogravimetric analysis (TGA), Fourier transform infrared spectroscopy (FTIR), Raman and transmission electron microscopy (TEM) studies. MWCNTs have a high ASNase loading capacity, with a maximum immobilization yield of 90%. The adsorbed ASNase retains 90% of the initial enzyme activity at the optimized conditions (pH 8.0, 60 min, and 1.5 × 10-3 g mL-1 of ASNase). According to these results, ASNase immobilized onto MWCNTs can find improved applications in several areas, namely biosensors, medicine and food industry.

Efficient removal of parabens from real water matrices by a metal-free carbon nitride photocatalyst.

Metal-free graphite-like carbon nitride (GCN-500) was obtained by thermal post-treatment of bulk polymeric carbon nitride at 500 °C. The catalyst was thoroughly characterized by morphological, optical and textural analysis techniques. The efficiency of GCN-500 was evaluated under visible (λexc = 417 nm) LED excitation for the photocatalytic degradation of methyl-, ethyl- and propyl-paraben in different water matrices either isolated or in a mixture of the three compounds. The GCN-500 proved to be more efficient than the benchmark TiO2 P25, with complete conversion of the individual parabens within 20 min of irradiation, contrasting with 120 min needed for total degradation using TiO2. Experiments in the presence of selected scavengers confirmed the high importance of superoxide radicals in the photocatalytic oxidation of parabens using GCN-500. The effect of the nature of the aqueous matrix in the kinetics of the photocatalytic process was assessed using ultrapure, tap and river waters spiked with a mixture of the three parabens. Although still very efficient, the complexity of the real water samples turned the degradation process slower due to the presence of other components such as ions and dissolved organic matter. GCN-500 proved to be stable in a continuous-flow system using GCN-500 coated glass rings (GCN-500-GR) to remove MP, EP and PP from real water matrices.

ß-Cyclodextrin as a Precursor to Holey C-Doped g-C3 N4 Nanosheets for Photocatalytic Hydrogen Generation.

A green, template-free and easy-to-implement strategy was developed to access holey g-C3 N4 (GCN) nanosheets doped with carbon. The protocol involves heating dicyandiamide with ß-cyclodextrin (ßCD) prior to polymerization. The local symmetry of the GCN skeleton is broken, yielding CxGCN (x corresponds to the initial amount of ßCD used) with pores and a distorted structure. The electronic, emission, optical and textural properties of the best-performing material, C2GCN, were significantly modified as compared to bulk GCN. The spectroscopic and luminescent features of C2GCN show the characteristic π-π* electronic transition of GCN, accompanied by much stronger n-π* electronic transitions owing to the porous and distorted network. These new electronic transitions, along with the presence of additional carbon synergistically contributed to enhanced visible light absorption and restrained recombination of electron-hole pairs. Steady-state and time-resolved photoluminescence showed an effective quench of the fluorescence emission, accompanied by a decrease of fluorescence lifetime of C2GCN (2.20 ns) in comparison with GCN (5.85 ns), owing to the delocalization of electron and holes to new recombination centers. The photocatalytic activity of C2GCN was attributed to efficient charge carrier separation and improved visible-light absorbing ability. As result, C2GCN exhibited ∼5 times higher photocatalytic H2 generation under visible light than bulk GCN.

Catalytic and Photocatalytic Nitrate Reduction Over Pd-Cu Loaded Over Hybrid Materials of Multi-Walled Carbon Nanotubes and TiO2.

TiO2 and carbon nanotube-TiO2 hybrid materials synthesized by sol-gel and loaded with 1%Pd-1%Cu (%wt.) were tested in the catalytic and photocatalytic reduction of nitrate in water in the presence of CO2 (buffer) and H2 (reducing agent). Characterization of the catalysts was performed by UV-Vis and fluorescence spectroscopy, X-ray diffraction, temperature programed reduction, N2 adsorption, and electron microscopy. The presence of light produced a positive effect in the kinetics of nitrate removal. Higher selectivity toward nitrogen formation was observed under dark condition, while the photo-activated reactions showed higher selectivity for the production of ammonium. The hybrid catalyst containing 20 %wt. of carbon nanotubes shows the best compromise between activity and selectivity. A mechanism for the photocatalytic abatement of nitrate in water in the presence of the hybrid materials was proposed, based in the action of carbon nanotubes as light harvesters, dispersing media for TiO2 particles and as charge carrier facilitators.

Laccase immobilization over multi-walled carbon nanotubes: Kinetic, thermodynamic and stability studies.

The biocatalytic performance of immobilized enzyme systems depends mostly on the intrinsic properties of both biomolecule and support, immobilization technique and immobilization conditions. Multi-walled carbon nanotubes (MWCNTs) possess unique features for enzyme immobilization by adsorption. Enhanced catalytic activity and stability can be achieved by optimization of the immobilization conditions and by investigating the effect of operational parameters. Laccase was immobilized over MWCNTs by adsorption. The hybrid material was characterized by Fourier transformed infrared (FTIR) spectroscopy, scanning and transmission electron microscopy (SEM and TEM, respectively). The effect of different operational conditions (contact time, enzyme concentration and pH) on laccase immobilization was investigated. Optimized conditions were used for thermal stability, kinetic, and storage and operational stability studies. The optimal immobilization conditions for a laccase concentration of 3.75µL/mL were a pH of 9.0 and a contact time of 30min (522 Ulac/gcarrier). A decrease in the thermal stability of laccase was observed after immobilization. Changes in ΔS and ΔH of deactivation were found for the immobilized enzyme. The Michaelis-Menten kinetic constant was higher for laccase/MWCNT system than for free laccase. Immobilized laccase maintained (or even increased) its catalytic performance up to nine cycles of utilization and revealed long-term storage stability.

Continuous flow photo-Fenton treatment of ciprofloxacin in aqueous solutions using homogeneous and magnetically recoverable catalysts.

The degradation of ciprofloxacin was studied in aqueous solutions by using a continuous flow homogeneous photo-Fenton process under simulated solar light. The effect of different operating conditions on the degradation of ciprofloxacin was investigated by changing the hydrogen peroxide (0-2.50 mM) and iron(II) sulphate (0-10 mg Fe L(-1)) concentrations, as well as the pH (2.8-10), irradiance (0-750 W m(-2)) and residence time (0.13-3.4 min) of the process. As expected, the highest catalytic activity in steady state conditions was achieved at acidic pH (2.8), namely 85 % of ciprofloxacin conversion, when maintaining the other variables constant (i.e. 2.0 mg L(-1) of iron(II), 2.50 mM of hydrogen peroxide, 1.8 min of residence time and 500 W m(-2) of irradiance). Additionally, magnetite magnetic nanoparticles (ca. 20 nm of average particle size) were synthesized, characterized and tested as a possible catalyst for this reaction. In this case, the highest catalytic activity was achieved at natural pH, namely a 55 % average conversion of ciprofloxacin in 1.8 min of residence time and under 500 W m(-2). Some of the photocatalytic activity was attributed to Fe(2+) leaching from the magnetic nanoparticles to the solution.