The fabrication of TiO2 supported on slag-made calcium silicate as low-cost photocatalyst with high adsorption ability for the degradation of dye pollutants in water

Application of common industrial solid waste in water treatment: a review

Industrial solid waste has a wide range of impacts, and it is directly or indirectly related to land, atmosphere, water, and other resources. Industrial solid waste has a large amount of production, complex and diverse components and contains a variety of harmful substances. However, as industrial by-products, it also has a lot of available value. Industrial solid waste has been continuously studied in water treatment due to its special composition and porous and loose structure. It is known that there are few reviews of various industrial solid wastes in the field of wastewater treatment, and most of them only discuss single industrial solid waste. This paper aims to sort out the different studies on various solid wastes such as fly ash, red mud, wastewater sludge, blast furnace slag and steel slag in dyeing, heavy metal, and phosphorus-containing wastewater. Based on the modification of industrial solid waste and the preparation of composite materials, adsorbents, coagulants, catalysts, filtration membranes, geological polymers, and other materials with high adsorption properties for pollutants in wastewater were formed; the prospect and development of these materials in the field of wastewater were discussed, which provides some ideas for the mutual balance of environment and society. Meanwhile, some limitations of solid waste applications for wastewater treatment have been put forward, such as a lack of further researches about environment-friendly modification methods, application costs, the heavy metal leaching, and toxicity assessment of industrial solid waste.

Utilization of ferrous slags as coagulants, filters, adsorbents, neutralizers/stabilizers, catalysts, additives, and bed materials for water and wastewater treatment: A review

Solid waste is currently produced in substantial amounts by industrial activities. While some are recycled, the majority of them are dumped in landfills. Iron and steel production leaves behind ferrous slag, which must be created organically, managed wisely and scientifically if the sector is to remain more sustainably maintained. Ferrous slag is the term for the solid waste that is produced when raw iron is smelted in ironworks and during the production of steel. Both its specific surface area and porosity are relatively high. Since these industrial waste materials are so easily accessible and offer such serious disposal challenges, the idea of their reuse in water and wastewater treatment systems is an appealing alternative. There are many components such as Fe, Na, Ca, Mg, and silicon found in ferrous slags, which make it an ideal substance for wastewater treatment. This research investigates the potential of ferrous slag as coagulants, filters, adsorbents, neutralizers/stabilizers, supplementary filler material in soil aquifers, and engineered wetland bed media to remove contaminants from water and wastewater. Ferrous slag may provide a substantial environmental risk before or after reuse, so leaching and eco-toxicological investigations are necessary. Some study revealed that the amount of heavy metal ions leached from ferrous slag conforms to industrial norms and is exceedingly safe, hence it may be employed as a new type of inexpensive material to remove contaminants from wastewater. The practical relevance and significance of these aspects are attempted to be analyzed, taking into account all recent advancements in the fields, in order to help in the development of informed decisions about future directions for research and development related to the utilization of ferrous slags for wastewater treatment.

Synergetic adsorption-photocatalysis process for water treatment using TiO2 supported on waste stainless steel slag

This study presents an economical and efficient method to decolourise dye wastewater using industrial waste stainless steel slag (SSS). Titanium dioxide was immobilised on SSS by a precipitation-calcination method. Samples with different TiO₂ loadings (prepared using either titanium isopropoxide precursor or commercial TiO₂ nanoparticles) were used to decolourise an organic contaminant (methylene blue) under dark and UV conditions in aqueous solution, and their adsorption and photocatalytic performances were compared. Samples with 15 and 25 TiO₂ wt% prepared by the precursor method had normalised photocatalytic efficiencies per gram close to that of bare TiO₂; using an adsorption-photocatalysis process led to efficiencies 4.4 and 1.6 times higher than that of pure TiO₂. The improvement in catalytic performance (greater for samples with less than 50% TiO₂ content) may be due to better UV absorption ability (related to with the improvement of TiO₂ particle dispersion) and the close TiO₂ support interaction, which can eventually cause a photocatalysis-enhancing shift towards more negative oxidation potentials. The SSS also acted as an efficient adsorption trap for organic compounds. The pollutant was thus transferred to the TiO₂ surface and photodegraded more rapidly and efficiently. The outstanding synergetic adsorption-photocatalysis capacities of TiO₂ waste stainless steel slag composites for dye water treatment made the proposed conversion approach have great potential in practical applications.

Investigation of Dye Removal Capability of Blast Furnace Slag in Wastewater Treatment

Blast Furnace Slag (BFS) is a by-product of the iron ore processing industry with potential to be used in different industrial applications. In this research, BFS was used to examine its ability for dye removal from wastewater. The efficiency of two types of BFS samples for removal of cationic methylene blue (MB) and acidic methyl orange (MO) dyes was investigated and results found that the optimal conditions for treatment of wastewater were 80 g/L of adsorbent dose and 1 h of treatment time for both dyes. BFS was found to be more effective for removal of the acidic MO dye than the cationic MB dye. Under shorter residence times, the results showed reverse trends with BFS samples removing higher concentrations of MB than MO. The BFS chemistry had additional impacts on the efficiency of dye removal. Higher basicity of BFS had lower dye removal ability for adsorption of acidic dye when applied at smaller concentrations, while for cationic dye when applied at higher concentrations. The results showed that BFS has potential role for pre-treatment of industrial wastewater contaminated with dyes and may contribute to reduced use of more expensive adsorbents, such as activated carbons.

Unravelling the interfacial interaction in mesoporous SiO2@nickel phyllosilicate/TiO2 core-shell nanostructures for photocatalytic activity

Core-shell based nanostructures are attractive candidates for photocatalysis owing to their tunable physicochemical properties, their interfacial contact effects, and their efficacy in charge-carrier separation. This study reports, for the first time, on the synthesis of mesoporous silica@nickel phyllosilicate/titania (mSiO₂@NiPS/TiO₂) core-shell nanostructures. The TEM results showed that the mSiO₂@NiPS composite has a core-shell nanostructure with a unique flake-like shell morphology. XPS analysis revealed the successful formation of 1:1 nickel phyllosilicate on the SiO₂ surface. The addition of TiO₂ to the mSiO₂@NiPS yielded the mSiO₂@NiPS/TiO₂ composite. The bandgap energy of mSiO₂@NiPS and of mSiO₂@NiPS/TiO₂ were estimated to be 2.05 and 2.68 eV, respectively, indicating the role of titania in tuning the optoelectronic properties of the SiO₂@nickel phyllosilicate. As a proof of concept, the core-shell nanostructures were used as photocatalysts for the degradation of methyl violet dye and the degradation efficiencies were found to be 72% and 99% for the mSiO₂@NiPS and the mSiO₂@NiPS/TiO₂ nanostructures, respectively. Furthermore, a recyclability test revealed good stability and recyclability of the mSiO₂@NiPS/TiO₂ photocatalyst with a degradation efficacy of 93% after three cycles. The porous flake-like morphology of the nickel phyllosilicate acted as a suitable support for the TiO₂ nanoparticles. Further, a coating of TiO₂ on the mSiO₂@NiPS surface greatly affected the surface features and optoelectronic properties of the core-shell nanostructure and yielded superior photocatalytic properties.

The effect of graphitized carbon on the adsorption and photocatalytic degradation of methylene blue over TiO2/C composites

The TiO₂/C composites with approximately 40 wt% of carbon were prepared by calcination of precursors, formed from a one-pot liquid phase reaction between Ti(SO₄)₂ and flour. All TiO₂/C composites displayed mesoporous structures with high BET surface areas (117-138 m² g^-1) and small crystal sizes of TiO₂ (8-27 nm). The contents of graphitic carbon and rutile TiO₂ increased, while the surface area and TiO₂ crystal size decreased for the TiO₂/C composite on increasing the calcination temperature from 650 to 800 °C; when calcinated at 800 °C, the anatase TiO₂ completely changed into rutile TiO₂ in the TiO₂/C composite. The TiO₂/C composite calcinated at higher temperatures exhibited better adsorptive and photocatalytic degradation performance in the removal of methylene blue (MB). For the entire rutile TiO₂/C-800 composite, the adsorption process of MB can be well described by the pseudo-second-order kinetic model and is governed by chemical adsorption with the maximum adsorption capacity value equal to about 15 mg g^-1. Under continuous illumination with a 254 nm UV lamp (15 W) for 3 h, the percentage of MB (14 mg l^-1) photocatalytic degradation on 50 mg of TiO₂/C-800 was 25.1% higher than that of the maximum adsorption removal. These results suggest that the graphitized carbon has a significant effect on the adsorptivity and photocatalytic activity of the TiO₂/C composite.

From coordination polymer to carbon nanotube: Preparation, characterization and rapid adsorption capacity toward organic pollutants

A CuI coordination polymer based on the N,N’-bis(3-pyridinecarboxamide)-1,4-butane (3-dpyb) ligand, namely [Cu(3-dpyb)0.5Cl], is hydrothermally synthesized and structurally characterized, and is used as a catalyst precursor to synthesize multi-walled carbon nanotubes. Interestingly, the as-grown multi-walled carbon nanotubes exhibit high performance in removing dyes from solution and can serve as a low-cost and fast adsorbent. In addition, the adsorption behavior of this new adsorbent fits well with the Freundlich isotherm and the pseudo-second-order kinetic model.

Hybridization of CuO with Bi2MoO6 Nanosheets as a Surface Multifunctional Photocatalyst for Toluene Oxidation under Solar Irradiation

Herein, CuO/Bi₂MoO₆ hybrid nanosheets were prepared as a surface multifunctional photocatalyst for gas-phase toluene oxidation with high conversion (>99%). Aberration-corrected scanning transmission electron microscopy suggested that CuO species were highly dispersed on the nanosheets. X-ray absorption fine structure spectra indicated that the distorted and stretched Cu-O coordination structures in CuO/Bi₂MoO₆ nanosheets would provide open active sites. In situ Fourier transform infrared and density functional theory results showed that toluene molecules could be chemisorbed and activated on the active sites of CuO/Bi₂MoO₆ nanosheets by the C-H group forming CuO/Bi₂MoO₆···Ph-CH₃ surface complex compounds. These would induce electron-hole transfer and initiate photocatalytic reactions under visible light irradiation. The corresponding intermediates of benzaldehyde and benzoic acid would be detected by in situ diffuse reflectance infrared Fourier transform spectroscopy. Furthermore, the synergistic effect of CuO and Bi₂MoO₆ nanosheets could monitor charge dynamics to facilitate their respective transmission from photoexcitation sites to active centers. This work provides new insights into the essence of visible-light-driven surface photocatalysis and is expected to promote the design of novel and more effective photocatalysts at the molecular level.

Metallurgical Wastes Employed as Catalysts and Photocatalysts for Water Treatment: A Review

Metallurgical slags are a mass-produced industrial solid waste, often destined to landfills; the volumes disposed represent an environmental burden. Over the last three decades, applications have been found for these wastes, mainly as a low-cost additive in building materials. More recently, their unique chemical properties have attracted attention to produce high-added-value materials for environmental applications, to be used as adsorbents, catalysts, or a source of reactive species in environmental engineering. Such uses can be classified as a function of the added value generated, technological complexity, and environmental impact. This review will focus specifically on the modification and use of slags for catalysis, photocatalysis, and photocatalytic production of hydrogen, which have received relatively little attention in literature. A summary will be presented about the general requirements for using unmodified slags as well as slag processed under alkaline or acidic conditions for advanced oxidation processes. Then, an overview will be given of the use of slags as photocatalysts in water treatment, organized according to the origin of the product (steel, copper, magnesium, ferromanganese), as well as emerging reports on the photocatalytic production of hydrogen, in contrast to the use of highly specific titania-based products developed for the same purpose.

Towards visible-light photocatalysis for environmental applications: band-gap engineering versus photons absorption-a review

A range of different studies has been performed in order to design and develop photocatalysts that work efficiently under visible (and near-infrared) irradiation as well as to improve photons absorption with improved reactor design. While there is consensus on the importance of photocatalysis for environmental applications and the necessity to utilized solar irradiation (or visible-light) as driving force for these processes, it is not yet clear how to get there. Discussion on the future steps towards visible-light photocatalysis for environmental application is of great interest to scientific and industrial communities and the present paper reviews and discusses the two main approaches, band-gap engineering for efficient solar-activated catalysts and reactor designs for improved photons absorption. Common misconceptions and drawbacks of each technology are also examined together with insights for future progress.

Sensitization of TiO2 nanosheets with Cu-biphenylamine framework to enhance photocatalytic degradation performance of toxic organic contaminants: synthesis, mechanism and kinetic studies

TNS/Cu(X) composite materials were firstly synthesized via simple overnight stirring of TNS in the methanolic solution of Cu complexes. The developed TNS/Cu(X) composites had a well-designed nanostructure, in which the TNS and Cu complexes were closely bounded with each other. The biphenylamine complexes fixed on the TNS surface in form of nanocapsules, which were confirmed by TEM and SEM, thus improving the surface area and subsequently charge separation. Innovatively merged photocatalysts of Cu complexes with TNS were successfully verified for photocatalytic mineralization of colored and colorless organic contaminants under the visible light degradation. As compared to original TNS, TNS/Cu(BA) showed prominent improvement in the catalytic actions. Kinetics i.e. t _1/2 (half-life times period), K _app, and R ² (linear regression co-efficient) were also studied. The amended materials created charge separation, by means of electrons gathering at the higher CB, and holes gathering at the lower level valence band of the Cu complex, therefore improving mineralization efficiency of the electrons and holes. TNS/Cu(BA) degrade 99%-99.6% of methyl orange (MO) and rhodamine B (RhB) dyes at 120 min, and 160 min, respectively, and 68% of phenol and 53% of TCP were destroyed in 180 min. The resilient holes can directly destroy MO, RhB, phenol, and TCP.

Synthesis of thorium–ethanolamine nanocomposite by the co-precipitation method and its application for Cr(vi) removal

Studies on the adsorption of Cr(vi) from water by a thorium ethanolamine nanocomposite.

Activated electric arc furnace slag as an effective and reusable Fenton-like catalyst for the photodegradation of methylene blue and acid blue 29

In this work, an activated electric arc furnace slag (A-EAFS) was investigated as an effective Fenton catalyst for the photodegradation of methylene blue (MB) and acid blue 29 (AB29). Fourier transform infrared spectroscopy and UV-visible absorption analyses indicated that A-EAFS offers additional Fe₃O₄ because of the changes in the iron oxide phase and the favorable response to visible light. It has been found that the highest degradation efficiency can reach up to 94% for MB under optimal conditions of 1 g L^-1 of A-EAFS, 20 mM H₂O₂, and pH 3. The optimal conditions for AB29 were 0.1 g L^-1 A-EAFS, 4 mM H₂O₂, and pH 3 to reach 98% degradation efficiency. Visible light enhanced the degradation of both dyes. In addition, A-EAFS, could be easily separated magnetically, exhibited good chemical stability after seven successive photodegradation cycles.

Preparation of hollow Nd/TiO2 sub-microspheres with enhanced visible-light photocatalytic activity

Hollow Nd/TiO₂ sub-microspheres with enhanced visible-light photocatalytic activity are synthesised by employing carbon spheres as the template.

Facile synthesis of silver nanoparticles deposited on a calcium silicate hydrate composite as an efficient bactericidal agent

Silver nanoparticles deposited calcium silicate hydrate composite was synthesized and demonstrated high antibacterial activities against Gram-negative and Gram-positive bacteria.