Accelerated photodegradation (minute range) of the commercial azo-dye Orange II mediated by Co3O4/Raschig rings in the presence of oxone

The accelerated discoloration of Orange II by an innovative Co3O4/Raschig ring photocatalyst (from now on Co3O4/RR) is feasible and proceeds to completion using oxone as an oxidant within the surprisingly short time of ∼5 min. The preparation of Co3O4 small clusters (2–10 nm in size) on RR is reported. The discoloration/mineralization of the azo-dye Orange II was carried out in a concentric coaxial photo-reactor and was a function of the Orange II and oxone concentrations, the solution pH and the recirculation rate. At bio-compatible pH-values, the concentration of Co-ions in solution after photocatalysis (15 min) was found to be between 0.5 and 2 ppm, within the limits allowed for treated waters. The generation of peroxide was observed as long as Orange II was still available in solution. By elemental analysis (EA), the amount of Co of the Raschig rings was determined to be ∼65% (w/w) before and after the photocatalysis. This confirms the stability observed during long-term operation of the Co3O4/RR catalyst. The sizes of the Co3O4 clusters on the RR surface were determined by transmission electron spectroscopy (TEM). A non-uniform distribution of Co3O4 particles on RR with sizes between 2 and 10 nm was found. The presence of Co-clusters on the RR-surface was confirmed by electron dispersive spectroscopy (EDS) showing 12.6% surface Co-enrichment before the photocatalysis and 18.8% surface enrichment after the photocatalysis. By confocal microscopy the irregularly thick shaped Co3O4 on the Raschig rings was analyzed. The most striking observation is very large shift of Co2p3/2 line from 779.6 eV at time zero to 782.2 eV within 10 min after due to the photocatalysis taking place. This indicates a strong reduction of electron density on the cobalt atoms of Co3O4/RR and providing the evidence for the strong oxidation properties of this catalyst

Photocatalytic discoloration of Methyl Orange on innovative parylene–TiO2 flexible thin films under simulated sunlight

Parylene films loaded with TiO2 are reported as hotocatalysts in azo dye discoloration processes. The TiO2 loading of the parylene film was 0.32% (w/w) and the amount of TiO2 on the film was about two orders of magnitude below the TiO2 added in suspension to discolore the same solution of Methyl Orange used as a probe. The parylene/TiO2 films showed a similar activity in the presence of O2 or H2O2 during the discoloration of dyes. This shows the efficient role of O2 as $e_{cb}^-$ scavenger. The photonic efficiency of the parylene/TiO2 film during the Methyl Orange discoloration was 0.04. Based on X-ray photoelectron spectroscopy (XPS) data, the TiO2 particles loaded on the parylene film were shown to be at first encapsulated in the polymer. After the encapsulation is broken, the TiO2 particles are fully exposed to the dye solution. The lack of surface intermediates like C-residues, N and S-species after the photocatalytic process implies an efficient decomposition of the dye at the catalyst interface. During the dye degradation carbonates and carboxylates were detected by XPS and Fourier transform infrared spectroscopy (FTIR) disappearing at the end of the discoloration process. Evidence is presented during the photocatalysis for the formation of a composite parylene/TiO2 film. The formation of this composite involves surface modification of parylene (partial lost of chlorine) in the outermost surface layer with concomitant densification of the TiO2 particles on the parylene film. The parylene film presented a side with high rugosity and one with low rugosity attaching different amounts of TiO2 in each case as observed by transmission electron microscopy (TEM)

Abatement of an Azo Dye on Structured C-Nafion/Fe-Ion Surfaces by Photo-Fenton Reactions Leading to Carboxylate Intermediates with a Remarkable Biodegradability Increase of the Treated Solution

A novel C-Nafton/Fe-ion structured fabric capable of mediating Orange II decomposition in Fenton-immobilized photoassisted reactions is presented. The catalyst preparation requires the right balance between the amount of the Nafion necessary to protect the C-surface and the minimum encapsulation of the Fe-cluster catalytic sites inside the Nafion to allow the photocatalysis to proceed. The C-Nafion/Fe fabric can be used up to pH 10 under light to photocatalyze the disappearance of Orange II in the presence of H2O2. The photocatalysis mediated by the C-Nafion/Fe-ion fabric increased with the applied light intensity and reaction temperature in the reaction needing an activation energy of 9.8 kcal/mol. This indicates that ion- and radical-molecule reactions take place during Orange II disappearance. The build up and decomposition of intermediate iron complexes under light involves the recycling of Fe2+ and was detected by infrared spectroscopy (FTIR). This observation, along with other experimental results, allows us to suggest a surface mechanism for the dye degradation on the C-Nafion/Fe-ion fabrics. The C-Nafion/Fe-ion fabric in the presence of H2O2 under solar simulated light transforms the totally nonbiodegradable Orange II into a biocompatible material with a very high BOD5/COD value. X-ray photoelectron spectroscopy (XPS) and sputtering by Ar+-ions of the upper surface layer of the C-Nafion/Fe-ion fabric allow us to describe the intervention of the photocatalyst down to the molecular level. Most of the Fe clusters examined by transmission electron microscopy (TEM) showed particle sizes close to 4 nm due to their encapsulation into the Gierke cages of the Nafion thin film observed by scanning electron microscopy (SEM) and optical microscopy (OM)

Preparation, stabilization and characterization of TiO2 on thin polyethylene films (LDPE): Photocatalytic applications

An innovative way to fix preformed nanocrystalline TiO2 on low-density polyethylene film (LDPE-TiO2) is presented. The LDPE-TiO2 film was able to mediate the complete photodiscoloration of Orange II using about seven times less catalyst than a TiO2 suspension and proceeded with a photonic efficiency of ~0.02. The catalyst shows photostability over long operational periods during the photodiscoloration of the azo dye Orange II. The LDPE-TiO2 catalyst leads to full dye discoloration under simulated solar light but only to a 30% TOC reduction since long-lived intermediates generated in solution seem to preclude full mineralization of the dye. Physical insight is provided into the mechanism of stabilization of the LDPE-TiO2 composite during the photocatalytic process by X-ray photoelectron spectroscopy (XPS). The adherence of TiO2 on LDPE is investigated by electron microscopy (EM) and atomic force microscopy (AFM). The thickness of the TiO2 film is seen to vary between 1.25 and 1.69 mm for an unused LDPE-TiO2 film and between 1.31 and 1.50 mmfor a sample irradiated 10h during Orange II discoloration pointing out to a higher compactness of the TiO2 film after the photocatalysis

Experimental feedback linearisation of a vibrating system with a non-smooth nonlinearity

Input-output partial feedback linearisation is demonstrated experimentally for the first time on a system with non-smooth nonlinearity, a laboratory three degrees of freedom lumped mass system with a piecewise-linear spring. The output degree of freedom is located away from the nonlinearity so that the partial feedback linearisation possesses nonlinear internal dynamics. The dynamic behaviour of the linearised part is specified by eigenvalue assignment and an investigation of the zero dynamics is carried out to confirm stability of the overall system. A tuned numerical model is developed for use in the controller and to produce numerical outputs for comparison with experimental closedloop results. A new limitation of the feedback linearisation method is discovered in the case of lumped mass systems e that the input and output must share the same degrees of freedom