Effects of Synthesis Parameters on Structure and Antimicrobial Properties of Bacterial Cellulose/Hydroxyapatite/TiO2 Polymer-Ceramic Composite Material

Bacterial cellulose (BC) is a highly pure polysaccharide biopolymer that can be produced by various bacterial genera. Even though BC lacks functional properties, its porosity, three-dimensional network, and high specific surface area make it a suitable carrier for functional composite materials. In the present study, BC-producing bacteria were isolated from kombucha beverage and identified using a molecular method. Two sets of the BC hydrogels were produced in static conditions after four and seven days. Afterwards, two different synthesis pathways were applied for BC functionalization. The first method implied the incorporation of previously synthesized HAp/TiO2 nanocomposite using an immersion technique, while the second method included the functionalization of BC during the synthesis of HAp/TiO2 nanocomposite in the reaction mixture. The primary goal was to find the best method to obtain the functionalized material. Physicochemical and microstructural properties were analyzed by SEM, EDS, FTIR, and XRD methods. Further properties were examined by tensile test and thermogravimetric analysis, and antimicrobial activity was assessed by a total plate count assay. The results showed that HAp/TiO2 was successfully incorporated into the produced BC hydrogels using both methods. The applied methods of incorporation influenced the differences in morphology, phase distribution, mechanical and thermal properties, and antimicrobial activity against Staphylococcus aureus (ATCC 25923), Escherichia coli (ATCC 25922), Proteus mirabilis (ATCC 12453), and Candida albicans (ATCC 10231). Composite material can be recommended for further development and application in environments that are suitable for diseases spreading.

Photocatalyst of manganese ferrite and reduced graphene oxide supported on activated carbon from cow bone for wastewater treatment

The present research aimed to evaluate the photocatalytic activity of manganese ferrite (M) and reduced graphene oxide (G) supported on pulverized activated carbon from cow bone waste (PAC-MG). PAC-MG was characterized by different instrumental techniques. The efficiency of PAC-MG was evaluated using solar irradiation under different conditions of photocatalyst concentration, H2O2 concentration, and pH ranges for the discoloration of methylene blue dye (MB). The synergy between the nanomaterials potentiated the photocatalytic activity, reaching 85.5% of MB discoloration when using 0.25 g L-1 of catalyst at neutral pH with no oxidant needed. Furthermore, PAC-MG demonstrated excellent stability in 6 consecutive cycles. Finally, it is expected that the present study can add value to industrial waste and contribute to the development of novel water and wastewater treatment methods, ensuring water quality for human consumption and the environment.

Charge transfer mechanism through S-scheme heterojunction in in-situ synthesized TiO2/Fe-doped hydroxyapatite for improved photodegradation of xanthate

The heterojunction structure of the photocatalyst composite, which necessitates a robust interface and sufficient contact areas, holds the key to obtaining high charge carrier migration efficiency. Here, a novel composite, TiO2 nanoparticles/Fe-doped hydroxyapatite (TONPs/FH_CS), is fabricated using a two-step synthetic technique, in which FH_CS is synthesized from artificial converter slag enriched with Fe and Ca. The unique nanorod@plate structure of FH_CS enables the uniform immobilization of TONPs onto FH_CS. Thereby, an n-n type heterojunction exhibits a highly intimate Ti-O-Fe heterointerface. Kelvin probe testing demonstrates the formation of an interfacial electric field oriented from FH_CS to TONPs, which serves as the driving force for interfacial electron transfer through the Ti-O-Fe channels. The photoacoustic signals provide information on electron trap levels and densities, indicating the formation of the electron transfer channels. •O2- and •OH species are responsible for being the active species in this system. A photoexcited carrier transfer pathway exhibiting an S-scheme mechanism with high separation efficiency significantly enhances the utilization of charge carriers in each phase. Thus, improved xanthate degradation has been achieved using a heterojunction containing a photocatalyst derived from industrial solid waste. This work demonstrates the significant potential of steel-making byproduct utilization in industrial wastewater treatment.

Volatile organic compounds (VOCs) removal by photocatalysts: A review

Amplified anthropogenic release of volatile organic compounds (VOCs) gets worse air quality and human health. Photocatalytic degradation of VOCs is the practical strategy due to its low cost, simplicity, high efficiency, and environmental sustainability. Different types of photocatalyst activated by UV and visible lights are applied for VOC degradation. This review tries to investigate the state-of-art of recently published papers on this subject with a focus on the high-efficiency photocatalyst. The novel photocatalysts are introduced and enhancing photocatalytic activity strategies such as the hybrid of two/three photocatalyst, impurity doping, and heterojunctions with narrow bandgap semiconductors have been explained. The procedures of visible light activation of the photocatalysts are discussed with attention to current problems and future challenges. In addition, effective operational parameters in the photocatalytic degradation of VOCs have been reviewed with their advantages and drawbacks. A series of strategies are developed for the efficient utilization of visible light photocatalysts and improving new materials or design structures to degrade produced toxic intermediates/by-products during photocatalytic degradation of VOCs. This review shows that there are significant challenges in the applications of photocatalysts in the selective removal of VOCs. Several approaches should be combined to produce synergistic effects, which may lead to much higher photocatalytic performance than individual strategies. Another challenge is to develop efficient photocatalysts to meet real problems on an industrial scale.

Recent Breakthrough in Layered Double Hydroxides and Their Applications in Petroleum, Green Energy, and Environmental Remediation

The fast development of the world civilization is continuously based on huge energy consumption. The extra-consumption of fossil fuel (petroleum, coal, and gas) in past decades has caused several political and environmental crises. Accordingly, the world, and especially the scientific community, should discover alternative energy sources to safe-guard our future from severe climate changes. Hydrogen is the ideal energy carrier, where nanomaterials, like layered double hydroxides (LDHs), play a great role in hydrogen production from clean/renewable sources. Here, we review the applications of LDHs in petroleum for the first time, as well as the recent breakthrough in the synthesis of 1D-LDHs and their applications in water splitting to H2. By 1D-LDHs, it is possible to overcome the drawbacks of commercial TiO2, such as its wide bandgap energy (3.2 eV) and working only in the UV-region. Now, we can use TiO2-modified structures for infrared (IR)-induced water splitting to hydrogen. Extending the performance of TiO2 into the IR-region, which includes 53% of sunlight by 1D-LDHs, guarantees high hydrogen evolution rates during the day and night and in cloudy conditions. This is a breakthrough for global hydrogen production and environmental remediation.

Biowaste derived hydroxyapatite embedded on two-dimensional g-C3N4 nanosheets for degradation of hazardous dye and pharmacological drug via Z-scheme charge transfer

In recent years, there has been an increase in demand for inexpensive biowaste-derived photocatalysts for the degradation of hazardous dyes and pharmacological drugs. Here, we developed eggshell derived hydroxyapatite nanoparticles entrenched on two-dimensional g-C₃N₄ nanosheets. The structural, morphological and photophysical behavior of the materials is confirmed through various analytical techniques. The photocatalytic performance of the highly efficient HAp/gC₃N₄ photocatalyst is evaluated against methylene blue (MB) and doxycycline drug contaminates under UV–visible light exposure. The HAp/gC₃N₄ photocatalyst exhibit excellent photocatalytic performance for MB dye (93.69%) and doxycycline drug (83.08%) compared to bare HAp and g-C₃N₄ nanosheets. The ultimate point to note is that the HAp/gC₃N₄ photocatalyst was recycled in four consecutive cycles without any degradation performance. Superoxide radicals play an important role in degradation performance, which has been confirmed by scavenger experiments. Therefore, the biowaste-derived HAp combined with gC₃N₄ nanosheets is a promising photocatalyst for the degradation of hazardous dyes and pharmacological drug wastes.

Manganese Ferrite-Hydroxyapatite Nanocomposite Synthesis: Biogenic Waste Remodeling for Water Decontamination

Environmental pollution, especially water pollution caused by dyes, heavy metal ions and biological pathogens, is a root cause of various lethal diseases in human-beings and animals. Water purification materials and treatment methods are overpriced. Consequently, there is an imperative outlook observance for cheap materials for the purification of wastewaters. In order to fill up the projected demand for clean water, the present study aimed to make use of cost-effective and environmentally friendly methods to convert bone-waste from animals such as cows into novel composites for the decontamination of water. The bone-waste of slaughtered cows from the Najran region of Saudi Arabia was collected and used for the synthesis of hydroxyapatite based on the thermal method. The synthesized hydroxyapatite (Ca₁₀(PO₄)₆(OH)₂) was utilized to prepare a manganese ferrite/hydroxyapatite composite. The nanocomposite was categorized by diverse sophisticated procedures, for instance XRD, FE-SEM, EDX, TEM, UV, PL and FT-IR. This composite possesses outstanding photocatalytic activity against methylene blue dye, which is a common pollutant from industrial wastes. Moreover, the synthesised composite revealed exceptional bacteriostatic commotion towards E. coli and S. aureus bacteria, which are accountable for acute waterborne infections. The outcome of this study demonstrated that the integration of manganese ferrite into hydroxyapatite significantly intensified both antimicrobial and photocatalytic actions when compared to the virgin hydroxyapatite.

Hydroxyapatite/TiO2 Nanomaterial with Defined Microstructural and Good Antimicrobial Properties

Due to the growing number of people infected with the new coronavirus globally, which weakens immunity, there has been an increase in bacterial infections. Hence, knowledge about simple and low-cost synthesis methods of materials with good structural and antimicrobial properties is of great importance. A material obtained through the combination of a nanoscale hydroxyapatite material (with good biocompatibility) and titanium dioxide (with good degradation properties of organic molecules) can absorb and decompose bacteria. In this investigation, three different synthesis routes used to prepare hydroxyapatite/titanium dioxide nanomaterials are examined. The morphology and semiquantitative chemical composition are characterized by scanning electron microscopy with energy dispersive X-ray analysis (SEM-EDX). The obtained materials’ phase and structural characterization are determined using the X-ray powder diffraction method (XRD). The crystallite sizes of the obtained materials are in the range of 8 nm to 15 nm. Based on XRD peak positions, the hexagonal hydroxyapatite phases are formed in all samples along with TiO₂ anatase and rutile phases. According to SEM and TEM analyses, the morphology of the prepared samples differs depending on the synthesis route. The EDX analysis confirmed the presence of Ti, Ca, P, and O in the obtained materials. The IR spectroscopy verified the vibration bands characteristic for HAp and titanium. The investigated materials show excellent antimicrobial and photocatalytic properties.

Photocatalytic performance of chitosan tethered magnetic Fe2O3-like (3D/2D) hybrid for the dynamic removal of anionic dyes: Degradation and mechanistic pathways

Efficient photocatalysis methods with a production of less number of toxic intermediates are extremely advantageous for water decontamination. The degradation efficiency, specific surface area, stability and porosity will be improving by wrapping of Fe₂O₃ using appropriate biopolymers. In this work, Fe₂O₃ reinforced chitosan (Fe₂O₃@CS) nanocomposite was fabricated using co-precipitation method. The chitosan makes available its surface for the useful generation of the nanocomposite. These wrapping of Fe₂O₃ on chitosan provides synergistically improved properties that could be attributed to the elevated partition efficiency and faster transfer of the photo-generated charge carriers, which was substantiated by the experimental outcomes from photoluminescence and ESR spectroscopy. The results obtained from DRS analysis entail the reduction in band gap of Fe₂O₃@CS (2.52 eV) as compared with 3.52 eV of Fe₂O₃. The results indicated that 89.2% and 94.6% were the maximum degradations correspondingly for MO and OG. The trapping investigation emphasized the involvement of OH radicals in the degradation of dyes over Fe₂O₃@CS composites. The five cycles of regeneration experiment recommended the superior photostability of the fabricated Fe₂O₃@CS composite. This work proposed a practical arrangement and subsequent influence of an advanced photocatalyst for the useful remediation dyes from contaminated water without causing any secondary pollution.

Hydroxyapatite, a multifunctional material for air, water and soil pollution control: A review

Hydroxyapatite (Ca₁₀(PO₄)₆(OH)₂), a calcium phosphate biomaterial, is a very promising candidate for the treatment of air, water and soil pollution. Indeed, hydroxyapatite (Hap) can be extremely useful in the field of environmental management, due in one part to its particular structure and attractive properties, such as its great adsorption capacities, its acid-base adjustability, its ion-exchange capability and its good thermal stability. Moreover, Hap is able to constitute a valuable resource recovery route. The first part of this review will be dedicated towards presenting Hap's structure and defining properties that result in its viability as an environmental remediation material. The second will focus on its use as adsorbent for wastewater and soil treatment, while indicating the mechanisms involved in this remediation process. Finally, the last part will impart all findings on Hap's applications in the field of catalysis, whether it be as catalyst, as photocatalyst, or as active phase support. Hence, all of the above will have served in showcasing the benefits gained by employing hydroxyapatite in air, water and soil clean-up.

Photoelectric-Responsive Extracellular Matrix for Bone Engineering

Using noninvasive stimulation of cells to control cell fate and improve bone regeneration by optical stimulation can achieve the aim of precisely orchestrating biological activities. In this study, we create a fast and repeatable photoelectric-responsive microenvironment around an implant using a bismuth sulfide/hydroxyapatite (BS/HAp) film. The unexpected increase of photocurrent on the BS/HAp film under near-infrared (NIR) light is mainly due to the depletion of holes through PO₄^3- from HAp and interfacial charge transfer by HAp compared with BS. The electrons activate the Na⁺ channel of mesenchymal stem cells (MSCs) and change the cell adhesion in the intermediate environment. The behavior of MSCs is tuned by changing the photoelectronic microenvironment. RNA sequencing reveals that when photoelectrons transfer to the cell membrane, sodium ions flux and the membrane potential depolarizes to change the cell shape. Meanwhile, calcium ions fluxed and FDE1 was upregulated. Furthermore, the TCF/LEF in the cell nucleus began transcription to regulate the downstream genes involved in osteogenic differentiation, which is performed through the Wnt/Ca²⁺ signaling pathway. This research has created a biological therapeutic strategy, which can achieve in vitro remotely, precisely, and noninvasively controlling cell differentiation behaviors by tuning the in vivo photoelectric microenvironment using NIR light.

Hydrothermal/solvothermal synthesis and treatment of TiO2 for photocatalytic degradation of air pollutants: Preparation, characterization, properties, and performance

Photocatalytic oxidation (PCO) is a well-known technology for air purification and has been extensively studied for removal of many air pollutants. Titanium dioxide (TiO₂) is the most investigated photocatalyst in the field of environmental remediation owed to its chemical stability, non-toxicity, and suitable positions of valence and conduction bands. Various preparation techniques including sol-gel, flame hydrolysis, water-in-oil microemulsion, chemical vapour deposition, solvothermal, and hydrothermal have been employed to obtain TiO₂ materials. Hydro-/Solvothermal (HST) synthesis, focus of the present work, can be defined as a preparation method in which crystal growth occurs in a solvent at relatively low temperature (<200 °C) and above atmospheric pressure. This paper aims to provide a comprehensive and critical review of current knowledge regarding the application of HST synthesis for fabrication of TiO₂ nanostructures for indoor air purification. TiO₂ nanostructures are categorized from the morphological standpoint (e.g. nanoparticles, nanotubes, nanosheets, and hierarchically porous) and discussed in detail. The influence of preparation parameters including hydrothermal time, temperature, pH of the reaction medium, solvent, and calcination temperature on physical, chemical, and optical properties of TiO₂ is reviewed. Considering the complex interplay among catalyst properties, a special emphasis is placed on elucidating the interconnection between various photocatalyst features and their impacts on photocatalytic activity.

An efficient strategy for full mineralization of an azo dye in wastewater: a synergistic combination of solar thermo- and electrochemistry plus photocatalysis

An efficient strategy for full mineralization of azo dye in wastewater.