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Propane dehydrogenation (PDH) to propene is an important alternative to oil-based cracking processes, to produce this industrially important platform chemical 1 , 2 . The commercial PDH technologies utilizing Cr-containing (refs. 3 , 4 ) or Pt-containing (refs. 5 – 8 ) catalysts suffer from the toxicity of Cr( vi ) compounds or the need to use ecologically harmful chlorine for catalyst regeneration 9 . Here, we introduce a method for preparation of environmentally compatible supported catalysts based on commercial ZnO. This metal oxide and a support (zeolite or common metal oxide) are used as a physical mixture or in the form of two layers with ZnO as the upstream layer. Supported ZnO x species are in situ formed through a reaction of support OH groups with Zn atoms generated from ZnO upon reductive treatment above 550 °C. Using different complementary characterization methods, we identify the decisive role of defective OH groups for the formation of active ZnO x species. For benchmarking purposes, the developed ZnO–silicalite-1 and an analogue of commercial K–CrO x /Al 2 O 3 were tested in the same setup under industrially relevant conditions at close propane conversion over about 400 h on propane stream. The developed catalyst reveals about three times higher propene productivity at similar propene selectivity. Propene is obtained through propane dehydrogenation using catalysts that are toxic, expensive or demanding to regenerate with ecologically harmful compounds, but the ZnO-based alternative reported here is cheap, clean and scalable.

Workers of tanneries, welding industries, factories manufacturing chromate containing paints are exposed to hexavalent chromium that increases the risk of developing serious adverse health effects. This review elucidates the mode of action of hexavalent chromium on blood and its adverse effects. Both leukocyte and erythrocyte counts of blood sharply decreased in Swiss mice after two weeks of intraperitoneal treatment with Cr (VI), with the erythrocytes transforming into echinocytes. The hexavalent chromium in the blood is readily reduced to trivalent form and the reductive capacity of erythrocytes is much greater than that of plasma. Excess Cr (VI), not reduced in plasma, may enter erythrocytes and lymphocytes and in rodents it induces microcytic anemia. The toxic effects of chromium (VI) include mitochondrial injury and DNA damage of blood cells that leads to carcinogenicity. Excess Cr (VI) increases cytosolic Ca activity and ATP depletion thereby inducing eryptosis. Se, vitamin C, and quercetin are assumed to have some protective effect against hexavalent chromium induced hematological disorders.

Hexavalent chromium is a highly noxious and mobile environmental pollutant primarily released through industrial activities such as tanning, electroplating, mining, and pigment manufacturing. Cr(VI) exhibits mutagenic and carcinogenic properties due to its strong oxidizing nature, and poses severe risks to soil health, aquatic ecosystems, and living organisms. Its high solubility facilitates leaching through soil matrices, resulting in groundwater contamination and long-term ecological damage. Although conventional physicochemical remediation techniques are effective, their high operational; cost, energy demand, and generation of secondary pollutants limit their sustainability. The present review explores bamboo, and invasive and fast-growing plant with high biomass productivity, as a sustainable alternative for the remediation of Cr(VI) contaminated soil and water bodies. The phytoremediation potential of bamboo is discussed with emphasis on chromium uptake, immobilization, rhizospheric interactions, and tolerance mechanisms in contaminated soils. Furthermore, the application of bamboo-derived materials, including biochar, hydrochar, activated carbon, charcoal, and chemically modified bamboo-based adsorbents, is critically evaluated for Cr(VI) removal from aqueous systems through adsorption, reduction, and stabilization mechanisms. Comparative insights into the performance of bamboo-based adsorbents relative to conventional commercial materials are also presented. Finally, existing challenges related to large-scale application, material regeneration, and ecological risks associated with bamboo invasiveness are highlighted, and future research directions focusing on bamboo-based composite and recyclable materials are proposed to enhance remediation efficiency while minimizing secondary environmental impacts.

Hexavalent chromium is very carcinogenic, and it is, therefore, important to remove it from wastewater prior to disposal. This study reports the photoreduction of Cr(VI) under simulated sunlight using graphene-derived TiO2 nanowire (TNW) composites. Electrophoretic deposition (EPD) of graphene oxide (GO) and reduced graphene oxide (rGO) was carried out on rutile phase TNWs. The TNWs were fabricated by thermal oxidation of titanium foil in the presence of 1M potassium hydroxide mist at 750 °C. The TNWs uniformly covered the surface of the titanium foil. EPD of GO or rGO was done as a function of time to produce deposits of different thicknesses. The photocatalytic performances of the GO/TNWs or rGO/TNWs were tested to reduce Cr(VI) under visible light. The performance of rGO/TNWs in reducing Cr(VI) was better than GO/TNWs. A 10-second-deposited rGO on TNW samples can reduce 10 mg/L Cr(VI) within 30 min under visible light, likely as a result of the high electron transfer from rGO to TNWs accelerating the Cr(VI) reduction.

In recent decades, environmental pollution with chromium (Cr) has gained significant attention. Although chromium (Cr) can exist in a variety of different oxidation states and is a polyvalent element, only trivalent chromium [Cr(III)] and hexavalent chromium [Cr(VI)] are found frequently in the natural environment. In the current review, we summarize the biogeochemical procedures that regulate Cr(VI) mobilization, accumulation, bioavailability, toxicity in soils, and probable risks to ecosystem are also highlighted. Plants growing in Cr(VI)-contaminated soils show reduced growth and development with lower agricultural production and quality. Furthermore, Cr(VI) exposure causes oxidative stress due to the production of free radicals which modifies plant morpho-physiological and biochemical processes at tissue and cellular levels. However, plants may develop extensive cellular and physiological defensive mechanisms in response to Cr(VI) toxicity to ensure their survival. To cope with Cr(VI) toxicity, plants either avoid absorbing Cr(VI) from the soil or turn on the detoxifying mechanism, which involves producing antioxidants (both enzymatic and non-enzymatic) for scavenging of reactive oxygen species (ROS). Moreover, this review also highlights recent knowledge of remediation approaches i.e., bioremediation/phytoremediation, or remediation by using microbes exogenous use of organic amendments (biochar, manure, and compost), and nano-remediation supplements, which significantly remediate Cr(VI)-contaminated soil/water and lessen possible health and environmental challenges. Future research needs and knowledge gaps are also covered. The review’s observations should aid in the development of creative and useful methods for limiting Cr(VI) bioavailability, toxicity and sustainably managing Cr(VI)-polluted soils/water, by clear understanding of mechanistic basis of Cr(VI) toxicity, signaling pathways, and tolerance mechanisms; hence reducing its hazards to the environment.

Vegetable cooking oil is used in domestic and commercial kitchens owing to its ability to modify and enhance the taste of the food through the frying process. However, as the oil is used through several frying cycles, it changes colour to dark brown and acquires an unpleasant smell. At this point, the waste oil is usually discarded, thereby finding its way into freshwater streams due to poor disposal and thus becoming an environmental pollutant. To provide an alternative, 'green' route to waste oil disposal, herein we repor t on the metal-free synthesis of onion-like nanocarbons (OLNCs) made from waste cooking oil via flame pyrolysis. The OLNCs were then applied in the removal of hexavalent chromium ions from aqueous solutions. The as-synthesised OLNCs were found to have similar proper ties (size, quasi-spherical shape etc.) to those synthesised from pure cooking oils. The Fourier-transform infrared spectroscopy data showed that the OLNCs contained C-O-type moieties which were attributed to the oxygenation process that took place during the cooking process. The OLNCs from waste oil were applied as an adsorbent for Cr(VI) and showed optimal removal conditions at pH = 2, t = 360 min, Co = 10 mg/L and Q0max = 47.62 mg/g, superior to data obtained from OLNCs prepared from pristine cooking oil. The results showed that the OLNCs derived from the waste cooking oil were effective in the removal of hexavalent chromium. Overall, this study shows how to repurpose an environmental pollutant (waste cooking oil) as an effective adsorbent for pollutant (Cr(VI)) removal.Significance: • Waste cooking oil outperformed olive oil as a starting material for the production of OLNCs for the removal of toxic Cr(VI) from water. • The superior performance of the OLNCs from waste cooking oil was attributed to the higher oxygen content found on their surface and acquired through the cooking process. • Not only are the OLNCs produced from waste cooking oil effective in the removal of Cr(VI), but they can be used multiple times before replacement, which makes them sustainable.

The hydrothermal synthesis is presented of copper-doped carbon dots (Cu-CDs) from citric acid, urea, and copper chloride, resulting in blue-fluorescent particles with stable emission at 438 nm when excited at 340 nm. Through comprehensive spectroscopic and microscopic characterization (FTIR, XPS, UV, and HRTEM), the Cu-CDs demonstrated remarkable stability across varying pH levels, ionic strengths, temperatures, and UV exposure. Notably, Cu-CDs exhibit ultra-sensitive and selective detection of hexavalent chromium [Cr(VI)] ions in aqueous environments driven by fluorescence quenching. The system showed a robust linear response to Cr(VI) in the 0–80 µM range, with an impressive limit of detection (LOD) of 0.186 µM, significantly lower than the WHO’s permissible limit of 0.96 µM. These findings position Cu-CDs as an effective tool for environmental monitoring and water safety applications. Graphical Abstract

The growing use of heavy metals in most industrial activities has led to it being considered as the most important environmental pollutant that may cause harm and toxicity to animals and humans. Chromium has been found in the environment in different oxidation states such as Cr 0 , Cr(III), and Cr(VI) and is released from a variety of anthropogenic and natural activities. At among, trivalent and hexavalent chromium are the most stable forms. Considerably, Cr(VI) is frequently more toxic than Cr(III) because of its particular solubility and high mobility. Chronic exposure and bioaccumulation of chromium, as a heavy metal, can cause toxicity and numerous pathophysiological defects, including allergic reactions, anemia, burns, and sores especially in the stomach and small intestine, damage to sperm along with the male reproductive system, and affect various biological systems. Chromium pollution can have severe consequences for water and the soil environment. This article reviews the toxicological effects of Cr(VI) and Cr(III) and their mechanisms of toxicity and carcinogenicity.

Microporous activated carbon was prepared from almond shell powder and activated with H3PO4 and was used for the removal of Cr (VI). The characterization of activated carbon was done for Fourier transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM), Brunauer–Emmett–Teller (BET) surface area measurement and elemental analysis. The batch experiments were conducted to study the effects of contact time, solution pH, adsorbent dose, initial chromium concentration and temperature on removal of Cr (VI). The Cr (VI) removal was found to be 100% at an initial pH of 2. The equilibrium data for the adsorption of Cr (VI) on the adsorbent were fitted with Langmuir, Freundlich, Temkin and Dubinin–Radushkevich adsorption isotherm models. The Langmuir isotherm model fitted better and values of model parameters qm, b, R2 and RL were found to be 195, 0.024, 0.98 and 0.45, respectively. Adsorption kinetics was analyzed for the pseudo first order, pseudo second order and intra-particle diffusion situations. Thermodynamic parameters revealed the spontaneous, endothermic and increased randomness nature of the adsorption process. The values of Δ H° and Δ S° were found to be 22.9 KJ/mol and 95.3 J/mol-K.

Hydroxypropyl chitosan-Cs 3 Bi 2 Cl 9 perovskite quantum dots (HPCS-PQDs) were synthesized by a simple ligand-assisted reprecipitation method via green hydroxypropyl chitosan as the ligand and used as the specific signal of a fluorescence probe to achieve the highly sensitive detection of hexavalent chromium (Cr(VI)) and compared with chitosan-Cs 3 Bi 2 Cl 9 QDs (CS-PQDs). HPCS-PQDs with multiple active hydroxyl passivations were found to enhance the photoluminescence quantum yield (PLQY) by 90%. After being placed in aqueous solution and irradiated with ultraviolet light for 96 h the fluorescence intensity of HPCS-PQDs remained above 60%. The blue emission of HPCS-PQDs has a good selectivity and short response time (30 s) for Cr(VI). A good linear relationship is established between the fluorescence quenching rate of the HPCS-PQDs and concentration of Cr(VI) from 0.8 to 400 µM, with a limit of detection (LOD) of 0.27 µM. The fluorescence quenching mechanism is the static quenching and internal filtration effect caused by HPCS-PQDs forming a non-fluorescent ground-state complex with Cr(VI). The sensor can not only be used to detect Cr(VI) in water samples with high accuracy but can also be prepared as a test paper for the detection for Cr(VI). Graphical Abstract