Preparation of novel iron-loaded microfibers entrapped carbon-nanotube composites for catalytic wet peroxide oxidation of m-cresol in a fixed bed reactor

Critical review on microfibrous composites for applications in chemical engineering

Microfibrous composites (MCs) are novel materials with unique structures and excellent functional properties, showing great potential in industrial applications. The investigation of the physicochemical properties of MCs is significant for accommodating the rapid development of high-efficiency chemical engineering industries. In this review, the characteristics, synthesis and applications of different types of previously reported MCs are discussed according to the constituent fibres, including polymers, metals and nonmetals. Among the different types of MCs, polymer MCs have a facile synthesis process and adjustable fibre composition, making them suitable for many complex situations. The high thermal and electrical conductivity of metal MCs enables their application in strong exothermic, endothermic and electrochemical reactions. Nonmetallic MCs are usually stable and corrosion resistant when reducing and oxidizing environments. The disadvantages of MCs, such as complicated synthesis processes compared to those of particles or powders, high cost, insufficient thorough study, and unsatisfactory regeneration effects, are also summarized. As a result, a more systematic investigation of MCs remains necessary. Despite the advantages and great application potential of microfibrous composites, much effort remains necessary to advance them to the industrial level in the chemical engineering industry.

Chemical removal of m-cresol: a critical review

m-Cresol containing wastewater has generally become a globally environmental issue due to its refractory and high toxicity towards plants, animals and human being. The development of m-cresol related industries increases the risk of excessive m-cresol discharge, making high efficiency methods to treat m-cresol an urgent topic in both economic and environmental aspects. This review focuses on the chemical treatment methods of m-cresol wastewater, including chemical adsorption, photocatalytic degradation, electrocatalytic degradation and catalytic wet oxidation. The efficiency, cost and process optimization of different methods are discussed in detail. Chemical adsorption is convenient but has relatively low efficiency. Photocatalytic degradation is an easily operated technology with high efficiency, but the selection of catalyst is too limited and the cost of light source is relatively high. Electrocatalytic degradation is time-saving but energy-intensive, and operational difficulty brings a barrier to industrialization. Catalytic wet oxidation (CWO) is highly effective and easily modified, but the performance and stability of catalysts are still very moderate. Following this, the selection and application of different methods regarding the requirement of actual environment are analyzed. Finally, a perspective on the opportunities and development for efficient m-cresol removal method is given.

New insights on the removal of diclofenac and ibuprofen by CWPO using a magnetite-based catalyst in an up-flow fixed-bed reactor

This research has been focused on the removal of two anti-inflammatory drugs, diclofenac (DCF) and ibuprofen (IBU), by a continuous catalytic wet peroxide oxidation (CWPO) process using a lab-synthesized nanomagnetic catalyst (Fe₃O₄/MWCNTs). The central composite rotatable design (CCRD) method was used to study the effect of DCF and IBU concentration (expressed as theoretical oxygen demand (ThOD) between 0 and 52.5 mg L^-1) and of the feed stream pH (from 3 to 7) on the removal of total organic carbon (TOC) and the concentration of aromatic compounds (Arm) and total phenolic compounds (TP) by CWPO. It could be observed that DCF was preferably removed from the DCF-IBU aqueous mixture at pH values ranging from 3 to 5. In addition, feed stream pH had a significant effect on the pollutants removal, as well as on TOC, TP and aromatic compounds removal, observing an increasing in the pollutants degradation when feed stream pH decreased from 7 to 3. Quadratic models predicted for response variable, such as TOC, TP and aromatic compounds removal, and their maximum model-predicted removal values were of 90.0, 80.2 and 90.0%, respectively. Finally, as a proof of concept, three environmentally-relevant aqueous matrices, spiked with DCF-IBU mixture, were treated. In this case, relatively high TOC degradation values were found after 20 h reaction time (ca. 57.7, 73.9 and 54.5% in surface water, WWTP effluent and hospital wastewater, respectively). This work deals the first study about DCF-IBU removal in aqueous solution by CWPO, as well as a continuous study using real wastewater that allow to extend the experimental results to a real scenario.

Great enhancement in phosphate uptake onto lanthanum carbonate grafted microfibrous composite under a low-voltage electrostatic field

Removal of phosphorus from water via cost-effective measures becomes important for water industry mainly due to eutrophication in waterbody. In our lab, a novel lanthanum carbonate-microfibrous composite (LC-MC) with good performance was previously synthesized for the removal of phosphorus. In this study, we further improved our technology by applying the electrostatic field (direct current, DC) to the adsorption system. It was showed that the applied DC can greatly improve the adsorption of phosphate in particular the adsorption capacity. Better removal was seen in the pH range of 5-9 at a higher temperature. The maximum adsorption capacity of 47.57 mg-PO₄^3- g^-1 was achieved, which was 1.4 times of that operated in the absence of applied DC. The adsorption equilibrium was established at the contact time of 240 min; the adsorption history was well described by the intraparticle surface diffusion model. The negative effect from oxygen-containing anions on the phosphate uptake followed the decreasing sequence of: humic acid > carbonate > nitrate > sulfate; on the other hand, the halogen anions had almost no influence on it. Finally, the mechanism study by XPS, XRD, and IR demonstrated that the ligand exchange played an important role in the electro-assisted phosphate uptake process.

An innovative lanthanum carbonate grafted microfibrous composite for phosphate adsorption in wastewater

Excessive presence of phosphorus in waters can cause eutrophication, a global unsolved environmental problem that has caused harmful effects to our eco-system and the source of our drinking water. In the study presented in this paper, a novel lanthanum carbonate grafted microfibrous composite (LC-MC) adsorbent was synthesized aiming at removing large amount of phosphate in wastewater efficiently. An optimized LC-MC was firstly prepared. The most suitable pH for the phosphate uptake was pH 7 to 9. The adsorption showed similar behavior in a wide range of ionic strength. The presence of co-existing anions was proved to have a less significant effect on the removal. The adsorption isotherm data were better fitted by the Freundlich isotherm than the Langmuir isotherm. The equilibrium was reached at about 300 min of contact time. 80 % of original adsorption capacity can be achieved even after 5 cycles of adsorption- desorption operations, indicating great regenerative performance of the adsorbent. The adsorption mechanism study showed that the ligand exchange played a key role during the phosphate adsorption.

Mathematical modelling of MS2 virus inactivation by Al/Fe-PILC-activated catalytic wet peroxide oxidation (CWPO)

Catalytic wet peroxide oxidation (CWPO) is a novel, alternative technology to conventional disinfection methods that are widely used to control microbial parameters in drinking water. To assess its effectiveness, new studies revealing the kinetics of MS2 coliphage inactivation by CWPO technology are required. This investigation therefore aimed to perform mathematical modelling of MS2 inactivation through CWPO technology activated by an Al/Fe-pillared clay catalyst (Al/Fe-PILC) in the presence of a synthetic surrogate of dissolved natural organic matter. The inactivation constant was obtained from two different statistical approaches, and the experimental data were better fitted to the pseudo-first-order Chick-Watson model in which the inactivation rate is constant. For this model, the maximum inactivation rate was k = 0.1648 min^-1, which was achieved in the MS2-3 catalytic test using an initial mass ratio of peroxide to active iron (Fe_act) of 1.2 mg H₂O₂/mg Fe_act. To estimate the inactivation rate due to reactive oxygen species (ROS), we supposed that the inactivation constant depends on both ROS and Fe_act. In this case, the maximum inactivation rate due to ROS was k_r = 2.4 × 10^-9 min^-1 (using 1.17 mg H₂O₂/mg Fe_act), which was achieved in the MS2-10 trial; both cases led to the conclusion that the optimal initial ratio of peroxide to active Fe in the catalyst in CWPO activated by Al/Fe-PILC was close to 1.2 mg H₂O₂/mg Fe_act. These kinetic studies showed that rapid inactivation takes place very early in the reaction, followed by slow inactivation during the remaining period of the recorded reaction time. This research revealed the strong potential of CWPO technology to improve microbiological parameters in drinking water due to the high catalytic performance in the heterogeneous Fenton reaction displayed by Fe sites incorporated in the Al/Fe-PILCs.

Iron-loaded carbon nanotube-microfibrous composite for catalytic wet peroxide oxidation of m-cresol in a fixed bed reactor

A kind of novel iron-loaded carbon nanotube-microfibrous composite (Fe₂O₃-CNT-MF) catalyst is prepared and tested for fixed bed m-cresol catalytic wet peroxide oxidation (CWPO) reaction. Results show that the Fe₂O₃-CNT-MF can significantly decline the pressure drop of the fixed bed. Higher temperature, lower feed flow rate, higher catalyst bed height, and higher H₂O₂ dosage are beneficial to m-cresol degradation. Lower pH can also improve m-cresol degradation, but it will cause severe iron leaching. The highest m-cresol removal (over 99.5%) and total organic carbon (TOC) removal (53.6%) can be observed under condition of 2 cm bed height, flow rate of 2 mL/min, reaction temperature of 70 °C, 6 g/L H₂O₂, and initial pH = 1. Meanwhile, the Fe₂O₃-CNT-MF catalyst shows good stability with less than 10% decrease in m-cresol conversion and 7% decrease in TOC conversion after 24-h reaction and less than 2 mg/L iron leaching is observed in all conditions except for strong acid condition. Two probable pathways of m-cresol degradation process are presented. Under most conditions, m-cresol will first be turned into methylhydroquinone, followed by oxidation to p-toluquinone. In basic condition, some m-cresol will first be changed into 4-methylpyrocatechol. These aromatic intermediates will then be oxidized into some small molecular acids and finally be mineralized to CO₂ and H₂O.