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In this study potassium salts such as KF, KCl and KBr were doped onto g-C3N4 to form KX-g-C3N4 (X = F, Cl and Br) via a thermal method. The KX-g-C3N4 was characterized by various instrumentation techniques such as UV-visible, FT-IR, XRD, Photoluminescence, TGA, BET, Raman, SEM, EDAX, HR-TEM, and Zeta potential. KX-g-C3N4 was explored for the photocatalytic degradation of methylene blue (MB) under visible light irradiation. Among them, KF-g-C3N4 showed excellent photocatalytic degradation of methylene blue (MB) under visible light irradiation. The KF-g-C3N4 significantly reduced the electrons-holes recombination rate when compared to KCl-g-C3N4, KBr-g-C3N4 and g-C3N4. The photocatalytic degradation mechanism was also studied with KF-g-C3N4.

Coal fly ash was decorated with a graphene oxide-tungsten oxide nanorods nanocomposite (CFA/GO/WO3NRs nanocomposite) via a hydrothermal method and applied for the remediation of lead (Pb2+ ions). The Pb2+ ion-loaded spent adsorbent (CFA/GO/WO3NRs + Pb2+ nanocomposite) was reused for the photodegradation of acetaminophen. CFA/GO/WO3NRs + Pb2+ nanocomposite displayed rapid removal of Pb2+ ions. Pseudo-second-order kinetics and the Langmuir isotherm model described the adsorption data. The adsorption capacity of the CFA/GO/WO3NRs nanocomposite was 41.51 mg/g for the removal of Pb2+ ions. Additionally, the Pb2+ ion-loaded spent adsorbent significantly influenced the degradation of acetaminophen by photocatalysis where 93% degradation was observed. It is worthy to note the reuse application of Pb2+ ion-loaded spent adsorbent as a photocatalyst, which will significantly reduce the secondary waste obtained from conventional adsorption methods.

This article describes the fabrication of electrochemical devices for the detection of a key environmental pollutant, 4-Nitrophenol (4-NPh). 4-NPh is a requirement for the synthesis of organophosphate pesticides. These pesticides are mostly used in the agricultural sector to obtain a high yield of agricultural products. The use of 4-NPh in the agricultural field results in poisonous levels of this compound in the soil and water. Different techniques have been used for its transformation by biological and chemical degradation. However, these strategies not only created highly toxic pollutant but also need fast operation and time consuming processes. In this background, we have reported a broad and efficient review of the electrochemical reduction of 4-NPh as a feasible alternate method. In this review paper, graphene oxide (GO), reduced graphene oxide (rGO), N-doped graphene oxide, functionalized graphene oxide, metallic nanoparticles coated graphene oxide, metal oxides covered on rGO, polymer functionalized graphene oxide and hybrids materials functionalized with graphene oxide (hydroxyl apatite and β-cyclodextrin) which have been fabricated on a glassy carbon electrode (GCE) to enhance the electrocatalytic reduction and increase the sensor activity of 4-NPh are discussed. We have also described the effects of a few interfering phenolic pollutants such as aminophenol, hydroquinone, o-nitrophenol (o-NPh), trinitrotoluene, trinitrophenol, 2, 4-dinitrophenol (4-DNPh) and nitrobenzene. In the paper, easy and more effective electrochemical methods for the detection of 4-NPh with graphene- based nanocomposites modified on GCE for 4-NPh detection are summarized and discussed.

This study reports a new approach of preparation of carbon dots coated on aluminum oxide nanofibers (CDs/Al2O3NFs) nanocomposite and reusing the spent adsorbent of lead (Pb2+) ions loaded adsorbent (Pb2+-CDs/Al2O3NFs) nanocomposite for latent fingerprint detection (LFP) after removing Pb2+ ions from aqueous solution. CDs/Al2O3NFs nanocomposite was prepared by using CDs and Al2O3NFs with adsorption processes. The prepared nanocomposite was then characterized by using UV–visible spectroscopy (UV–visible), Fourier transforms infrared spectroscopy (FTIR), Fluorescence, X-ray diffraction pattern (XRD), scanning electron microscope (SEM), Transmission electron microscopy (TEM), Energy-dispersive X-ray spectroscopy (EDS), Zeta potential, X-ray photoelectron spectroscopy (XPS). The average size of the CDs was 51.18 nm. The synthesized CDs/Al2O3NFs nanocomposite has proven to be a good adsorbent for Pb2+ ions removal from water with optimum pH 6, dosage 0. 2 g/L. The results were best described by the Freundlich Isotherm model. The adsorption capacity of CDs/Al2O3NFs nanocomposite showed the best removal of Pb2+ ions with qm = (177. 83 mg/g), when compared to the previous reports. This adsorption followed the pseudo-second order kinetic model. ΔG and ΔH values indicated spontaneity and the endothermic nature of the adsorption process. CDs/Al2O3NFs nanocomposite therefore showed potential as an effective adsorbent. The data were observed from adsorption–desorption after 6 cycles which showed good adsorption stability and re- usability of CDs/Al2O3NFs nanocomposite. Furthermore, the spent adsorbent of Pb2+-CDs/Al2O3NFs nanocomposite has proven to be sensitive and selective for LFP detection on various porous substrates. Hence Pb2+-CDs/Al2O3NFs nanocomposite can be reused as a good fingerprint labelling agent in LFP detection so as to avoid secondary environmental pollution by disposal of the spent adsorbent.

A europium salt-Na[Eu(5,5′-DMBP)(phen)3]·Cl3 (Eu(III)-CPLx) was prepared by using various precursors such as 5,5′-Dimethyl-2,2′-bipyridyl (5,5′-DMBP), 1,10-phenanthroline (phen) and europium chloride hexahydrate (EuCl3·6H2O) by a complexation method. The red emission fluorescent Na[Eu(5,5′-DMBP)(phen)3]·Cl3/D-Dextrose (Eu(III)-CPLx/D-Dex) composite was synthesized by using an adsorption method with Eu(III)-CPLx and D-Dextrose (D-Dex). The Eu(III)-CPLx and fluorescent (Eu(III)-CPLx/D-Dex) composites were characterized by numerous techniques. The fluorescent (Eu(III)-CPLx/D-Dex) composite demonstrated a strong red emission and controlled fluorescence quenching in the solid state and was consequently used in latent fingerprint (LFP) detection. The LFPs were developed by using a powder dusting method (PDM) with Eu(III)-CPLx and fluorescent Eu(III)-CPLx/D-Dex composites on different substrates under daylight and UV-light irradiation at 365 nm. The fluorescent Eu(III)-CPLx/D-Dex composite was effectively explored for developing LFP images on various substrates and also acts as a better labeling agent for LFP detection in forensic science crime scene investigations.

This study reports the first new approach of using nitrogen functionalized carbon dots coated on zinc oxide nanoparticles (N-CDs/ZnONPs) as a novel nanocomposite for latent fingerprint detection using the powder brushing method. N-CDs/ZnONPs nanocomposite was prepared using melamine, potato peel waste and zinc acetate dehydrate as precursors. This nanocomposite was characterized by Fourier-transform infrared spectroscopy, UV–Visible spectroscopy, Fluorescence spectroscopy, X-ray diffraction, Raman spectroscopy, Zeta nanosizer, Scanning Electron Microscope, Energy-Dispersive X-ray Spectrometry and Transmission Electron Microscopy. The size of N-CDs was around at 50–20 nm and ZnONPs was around at 40–50 nm. The quantum yield of N-CDs increased the fluorescence intensity of the fluorophore by 5.54%. The N-CDs were coated on surface of ZnONPs to increase the quantum yield and increase the blue emission after formation of N-CDs/ZnONPs by 5.12%.The N-CDs/ZnONPs nanocomposite demonstrated extraordinary sensitivity and selectivity for Latent Fingerprint (LPF) detection on the distinctive non-porous substrates which included aluminum foil, aluminum sheets, an aluminum rod, an iron disc, a compact disc, a black mat, white marble and magazine paper. This nanocomposite acts as a labeling agent and it helped to detect LFP with clear readability ridges and high contrast fingerprint images under UV light irradiation. N-CDs/ZnONPs nanocomposite additionally demonstrated superior ability to reveal readability ridges and clarity and high contrast LFP images with 415 nm and 450 nm light sources and a yellow filter by using a Living Image Microscope. This nanocomposite exhibited advantages such as improved efficiency, a non-toxic nature, good optical properties and good results in the LFP detection of the freshly applied fingerprints. N-CDs/ZnONPs nanocomposite is, therefore, a good alternative material for detection of latent fingerprints in crime investigations. Keywords: N-CDs/ZnONPs nanocomposite, Latent fingerprint detection, Powder method

Highlights • Recent trends in the use of biopolymers for remediation of heavy metals are reviewed. • Biopolymers include alginate, cellulose and lignin. • Reusability is discussed. • Reuse applications of the spent adsorbents are made. • Recommendations for reuse of spent adsorbents in latent fingerprint detection are made., Living organisms are created by carbohydrate biopolymers such as chitosan, carboxymethyl cellulose, alginate and lignin. These carbohydrate biopolymers have been extensively used for environmental applications because they are bio-degradable, bio-compatible, non-toxic and inexpensive. Recently, carbohydrate biopolymers have been used to prepare different nanocomposite adsorbents for treatment of wastewater. These adsorbents explored the removal effectiveness of inorganic pollutants from aqueous solution. This review article discusses the synthesis and application of chitosan, carboxymethyl cellulose, alginate and lignin nanocomposites as adsorbents for heavy metals. Toxic metals can be efficiently absorbed by cross-linkers, distributed in aqueous solutions of divalent heavy metal ions to examine their polymer absorption capacity. These nanocomposites were used for the adsorption of highly toxic metals such as Cd2+, Pb2+ and Zn2+ in water. To make heavy metal ion uptake more effective, more functionalization has been implemented such as blending, grafting, or mixing with different nanomaterials with an extra functional group. The integration of the second part into the main polymer chain not only adds functionality but also increases mechanical efficiency, one of the core criteria for adsorbent recyclability. The remediation method of metal ions from wastewater is cheaper as long as the adsorbent is reused. Furthermore, they exhibited good performance for the reuse of spent adsorbents after adsorption-desorption processes including latent fingerprint detection with nanomaterials by using the powder dusting method. Chitosan, carboxymethyl cellulose, alginate and lignin based nanocomposites have demonstrated better adsorption activities due to great physical and chemical properties for the chelation of heavy metals such as Cd2+, Pb2+ and Zn2+ from water and also higher regeneration with various eluents after several desorption-adsorption cycles. In addition, reuse of the spent adsorbents in latent fingerprint detection with different nanomaterials is discussed. Finally, this review article makes recommendations for future studies in light of environmentally favourable and economical applications.

In this study, coal fly ash coated with a carbon hybrid nanocomposite (CFA/C HNCPs) was synthesised using a hydrothermal method and applied for the adsorption of cadmium ions (Cd2+) from aqueous solution. The possibility of reusing the spent adsorbent (Cd2+ loaded adsorbent referred to CFA/C–Cd2+ HNCPs) for the photocatalytic degradation of methylene blue dye (MB) was also investigated. CFA/C HNCPs exhibited rapid adsorption of Cd2+ ions through a pseudo second order kinetics model whereas the data was well fitted by the Langmuir Isotherm model. In addition, the Cd2+ loaded spent adsorbent played an important role for the photocatalytic degradation of MB with a percentage degradation of 97.41%. Interestingly, this is a new approach for the reuse of Cd2+ adsorbed material for photocatalytic application, which has significant environmental impact for reduction of waste derived from conventional adsorption techniques.

Porous graphitic carbon nitride (pg-C3N4) was synthesized from bulk g-C3N4 (Bg-C3N4). First, bulk g-C3N4 was prepared by a thermal method with poly-condensation of melamine as a precursor. The pg-C3N4 was synthesized from Bg-C3N4 under ultrasonic treatment in a sulphuric acid medium. Thereafter, pg-C3N4 was combined with commercial silica gel (Slg) to give a fluorescent Slg/pg-C3N4 powder. These prepared materials were characterized by means of distinctive instrumental techniques consisting of UV–visible spectroscopy (UV–visible), fluorescence spectroscopy (FL), Fourier transform infrared spectroscopy (FT-IR) X-ray diffraction (XRD), Raman spectroscopy, Brunauer–Emmett–Teller (BET), scanning electron microscope (SEM), transmission electron microscopy (TEM) and live cell microscopy. The fluorescent Slg/pg-C3N4 powder was used as a labeling agent for the development of latent fingerprints (LFP) on different surfaces such as glass slides, aluminum foil, aluminum sheets, aluminum rods, a compact disc (CD), iron discs, coins, a tea cup and spoon. The LFP images were additionally captured through the use of ultraviolet radiation at 365 nm due to the fluorescent nature of the Slg/pg-C3N4 powder. The LFP images have been also investigated using different commercial powders such as ZnSO4, TiO2 and Iodine vapor for comparison with fluorescent Slg/pg-C3N4 powder. The Slg/pg-C3N4 powder was used to investigate the LFP images submerged in fresh water. Ultimately, the different fluorescent backgrounds of LFP images had been demonstrated using live cell microscopy with pg-C3N4 and Bg-C3N4. The fluorescent Slg/pg-C3N4 powder exhibited potential as a good labeling agent with excessive sensitivity, rapid detection and an eco-friendly nature. This fluorescent Slg/pg-C3N4 powder was also used to develop the LFP images under conditions that are likely to simulate real crime scenes to establish whether this material can be used in real forensic investigations.

Heavy metals are becoming a huge problem in the environment and lead is one of them. Lead is disposed into water systems from huge industries such as paint industry, mining, and electroplating. In this study, manganese oxide coated fly ash (MnO2-CFA) was synthesized and characterized. The BET surface area of CFA MnO2-CFA was 18.4196 m2/g, 3 times more than the raw CFA (5.9231 m2/g). Batch adsorption experiments indicated that the uptake of Pb2+ fitted well in a Elovich kinetics model while the adsorption isotherm best fitted the Langmuir model with a maximum adsorption capacity of 141 mg/g at 40 °C and a pH of 7. Thermodynamic parameters obtained proved that the adsorption of Pb2+ ions using the MnO2-CFA was endothermic and spontaneous. Furthermore, the adsorbent was highly selective towards Pb2+ in the presence of Mn2+, Zn2, Ni2+and Cd2+. The Pb2+ removal % from a real water sample spiked with 30 mg/L Pb2+ was found to be 83.33%. The spent adsorbent was further applied in latent fingerprint detection which showed that Pb2+-MnO2-CFA produced clearer latent finger print (LFP) images compared to MnO2-CFA. LFP images were still clear 8 days after application of the spent adsorbent, proving that Pb2+-MnO2-CFA is a promising labelling agent.

The semiconductor metal oxide consisting of TiO2 nanoparticles has been applied for the environmental remediation of toxic substances from environmental samples. TiO2 nanoparticles have been used as a photocatalyst for the degradation of organic pollutants in wastewater samples and have demonstrated potential as an effective photocatalyst. This includes applications for the decontamination of compounds from contaminated samples under both UV and visible light irradiation. Although these nanoparticles have been easily utilized for this application, the electron–hole recombination rate and bandgap energy level could be very high. There are therefore numerous reports on TiO2 nanoparticles coated onto biopolymers of chitosan, alginate, and carboxymethyl cellulose and conducting polymers of polypyrrole, polythiophene, and polyaniline to give polymer TiO2 nanocomposites as the photocatalyst. Such studies have been implemented for the photocatalytic degradation of organic dyes under UV and visible light irradiation in an attempt to improve the photocatalytic activity by lowering the electron–hole recombination rate and the bandgap energy. Moreover adsorptive photocatalytic degradation is favored since this provides a surface onto which the pollutants are adsorbed first and thereafter undergo photocatalytic degradation. This chapter therefore provides an overview of TiO2 as a photocatalyst with respect to its advantages and disadvantages. In a critical review in the recent trends on supporting TiO2, other support materials are discussed, and future research perspectives are also critically evaluated.

In recent years, metal oxide semiconductors have been explored as photocatalysts for the degradation of organic contaminants in water/wastewater. The uniqueness of these oxide materials is in their ability to harness energy in the UV/Vis range, their relative ease of synthesis, low cost, and their general high surface ratio to mass, etc. Thus, these materials have consequently drawn much profound interest in environment applications, particularly pharmaceutical drugs for photocatalytic degradation. Furthermore, the non-toxic nature of most metal oxide semiconductors means they are convenient for water treatment works, resulting in safe drinking water for humans and safe environments for aquatic mammals. Pharmaceuticals are emerging pollutants that are increasingly being found in water systems. They have been detrimental to the human and animal health. In this article, pharmaceutical drugs abatement from water via photocatalysis process using oxide-based advanced metals such as TiO2, ZnO, Fe2O3,WO3, and Bi2WO6 is discussed. Degradation of various drugs at laboratory scale have been assessed and examples cited. Various approaches to metal oxides modifications and synthesis methods to improve degradation efficiency have also been discussed. Effects of experimental/operational parameters in the degradation process have been compiled and compared. Finally, a short preview of degradation of pharmaceuticals pilot scales is also highlighted.

A simple and sensitive electrochemical method was developed to determine the concentration of Sudan I in chili powder based on silver nanoparticles decorated graphene oxide modified glassy carbon electrode (AgNPs@GO/GCE). The voltammetry behaviour of Sudan I on modified GCE was investigated in phosphate buffer medium (PBS) with various pH ranges and the electron transfer properties were studied. It is found that the AgNPs@GO/GCE can catalyse the reduction of azo group, N N followed by electrochemical oxidation of -OH group present in Sudan I dye molecule. Quantitative detection of Sudan I present in food products was carried out by amperometry method in which reduction potential was fixed at −0.77 V vs. Ag/AgCl. The amperometry method showed an excellent performance with a sensitivity of 6.83 μA mM−1 and a detection limit of 11.4 × 10−7 M L−1. A linear calibration graph was constructed in the ranging 3.90 × 10−6 to 3.19 × 10−5 M L−1. The method was successfully applied for the determination of Sudan I in red chili powder samples.