Hydroxyapatite composites with carbon allotropes:Preparation,properties,and applications

Hydroxyapatite(HA)and its composites with inorganic additives,dopants,and polymers is a rapidly developing branch in the materials chemistry.In particular,carbon allotropes are widely used in these composites being widely applied for medical purposes.Observing a gap of insufficient generalization of recent achievements in the field of the HA/Carbon composites,in this review we present the state of the art of the field of HA composites and hybrids with classic carbon allotropes and nanocarbons.These composites are known for carbon nanotubes,nanofibers,graphene and its oxidized forms,as well as,in a lesser grade,for graphite,fullerenes,nanodiamonds,carbon nanofoams,etc.These composites can be fabricated by a variety of classic and less-common methods,such as co-precipitation(with or without ultrasonic treatment),CVD,hot isostatic pressing,hydrothermal,spark plasma sintering,biomimetic mineralization,thermal and plasma spray,electrochemical and electrophoretic deposition,self-assembling,3D printing,electrospinning,and lyophilisation,among others.Combination of various synthesis techniques can be also carried out for composite preparation.Natural or synthetic HA can be used as it is for further interaction with carbon allotropes or it can be first prepared and then reacted with carbon counterpart;similarly,carbon allotropes can be introduced into the interaction with HA directly or they can be first synthesized,in particular from biomass.Resulting biocompatible composites can be produced in the form of coatings,powders,and scaffolds and can additionally contain quantitative amounts of third phases,frequently natural or synthetic polymers.In these composites,especially with O-containing functionalizing groups,HA disadvantages could be considerably decreased with simultaneous enhancement of mechanical properties,becoming similar to human bone,chemical stability and biocompatibility,as well as possessing antibacterial effect.GO→G reduction and higher HA decoration were observed in several experiments.The morphology of polymer-containing HA/GO composites can be tuned by variations of GO:polymer ratios.Predominant number of resulting applications of formed HA composites corresponds to the biomedical area,mainly for orthopedic applications/implants,osteoporosis treatment,myocardial,skin and dental regeneration,etc.Other important uses include applications as adsorbents for the elimination of impurities from wastewaters and/or removal/uptake of heavy metal cations,loading several medicines,and energy storage materials.Biocompatibility and hemocompatibility aspects of HA/Carbon composites are also discussed and future developments are proposed.

Porphyrins,phthalocyanines,and related covalent-organic frameworks in the photochemical and electrochemical water splitting:A review

In this review,the possibilities of photochemical and electrochemical water splitting(WS)using porphyrins,phthalocyanines,related macrocycles,and their metal complexes are discussed.Significant efforts are being carried out in order to develop novel and cheap methods for water decomposition to generate inexhaustible greener energy sources(molecular hydrogen)instead of oil and gas.The processes of WS in heterogeneous and homogeneous media require novel photo-and electrocatalysts,in particular those on macrocycle basis.A high WS efficiency has been observed for porphyrins and phthalocyanines,showing their suitability both for HER and OER processes are available using these relative compounds for WS purposes.Porphyrins can be used in photocatalytic and electrocatalytic WS processes both in their free forms or as metal porphyrins/porphyrinates,mainly loaded on various inorganic materials,such as Au NPs,C_(3)N_(4),GaP,KTaO_(3),GaP,and so on,as part of porphyrin-containing polymers or on electrode surface as modifying coatings,being sometimes better than commercial catalysts,such as Pt/C.Photocatalytic H2 evolution can be considerably depended on the shape of porphyrin particles;in particular,porphyrin nanowires can yield up to 20 times more H2 than its powder.In certain cases,both HER and OER can be driven in the same electrolyte using metal porphyrins.The capacity of metal porphyrins to generate ROS(in particular,singlet oxygen 1O_(2))under ultrasonic treatment is known and can be successfully used for H_(2)O_(2) and O_(2) generation.Phthalocyanines can be used in similar processes in free form or as composites with inorganic or organic counterparts,being immobilized on nanocarbons,metal oxides and salts,or simply dissolved in water acting in a homogeneous medium.An additional use of ultrasound can lead to better results due to the synergistic effect of the sonochemical treatment and light.Covalent-organic frameworks are also applied for WS purposes and are mainly based on a variety of N-containing ligands,such as triazine,β-ketoenamines,andβ-ketoamines,bipyridine,as well as some S-containing ligands.Metal complexes in WS processes are widely represented by ruthenium coordination compounds,being suitable for future commercial artificial photosynthesis,as well by copper and cobalt coordination compounds with phenantroline,porphyrazine,and related derivatives,being used as electrocatalysts in the form of homogenous molecular films on glassy carbon electrode or as a part of a homogeneous photocatalytic water reduction system for HER processes.The analysis of the photo(electro)catalytic activity of these macrocycles indicated that the Covalent-organic frameworks are highly promising catalysts for H2 evolution from WS.