Today’s water-treatment plants combine practices designed to cope individually with various types of purification challenges. In some cases, the solution to one has detrimental effects on others, e.g. disinfection by chlorination forming hazardous organic contaminants. Water-treatment plants have large ecological footprints and operational costs, making the availability of high-quality water in developing areas almost impossible, due to lack of resources and infrastructure. Indeed, >2 billion people are exposed to diseases caused by contaminated water. Clearly, bringing safe, clean drinking water to people’s homes is essential to a good quality of life. Clay minerals may offer technologies and innovative practices which would help to develop a reliable, low-maintenance device with a small environmental footprint that processes stream, lake, or pond water into high-quality potable water. The basis for such technologies has already been established and improved approaches are being introduced on an ongoing basis by clay scientists: nanocomposite pre-treatment and disinfection, photodegradation of organic pollutants using clay-based catalysts, polishing of inorganic contaminants, and removal of biological pathogens by adsorption or deactivation onto specifically designed clay-based filters, etc. This short review presents a vision for combining those technologies in a tandem system for the delivery of high-quality water that is low-maintenance, affordable, and environmentally sustainable for the benefit of mankind.

A novel Ag/AgBr/Nb2O5 heterojunction photocatalyst was successfully developed via a facile solvothermal method combined with deposition–precipitation. The morphology and composition of the Ag/AgBr/Nb2O5 photocatalyst were investigated by transmission electron microscopy and X-ray energy-dispersive spectrometry, respectively. The results showed that metallic Ag was formed on the surface of the AgBr by an in situ photoreaction. The low crystalline Nb2O5 (L-Nb2O5) substrate provides the photocatalyst with a high specific area and numerous active sites for catalysis, while the combination of the Ag/AgBr with L-Nb2O5 effectively facilitates the separation of photo-generated charge carriers. The photocatalytic activities of the samples were measured using the degradation of an aqueous solution of rhodamine B under different LEDs with UV (365 nm), yellow (595 nm), and white (400 nm ≤ λ ≤ 800 nm) light. The Ag/AgBr/L-Nb2O5 photocatalyst displayed a much higher photocatalytic activity than bare L-Nb2O5 under UV and visible-light irradiation.

Two novel porphyrins (5,10,15,20-tetra(3-(carboethoxymethyleneoxy)phenyl)porphyrin, H2TEPp and 5,10,15,20-tetra(3-(carboxymethyleneoxy)phenyl)porphyrin, H2TCPp) and their copper(II) porphyrins (CuTEPp, CuTCPp) were synthesized. With these porphyrins, four new porphyrin-sensitized TiO2 nanorod composites (H2TEPp/TiO2, H2TCPp/TiO2, CuTEPp/TiO2, and CuTCPp/TiO2) were prepared and characterized by methods of XRD, SEM, TEM, FT-IR, UV-vis DRS, nitrogen adsorption–desorption and fluorescence spectra. Besides, the photocatalytic activity and stability of the composites were assessed in the degradation of 4-nitrophenol (4-NP). The results indicate that the morphologies and structures of these composites are less influenced by the loaded porphyrins or copper porphyrins compared with the nanorods TiO2 (anatase). The porphyrin or copper porphyrin molecules are confirmed to bond on the surface of TiO2 through carboxyl group, which is beneficial to the electron transfer between porphyrin and TiO2. All composites exhibit enhanced photoactivities compared with the bare TiO2 nanorods. The possible reason is that the recombination of photoproduced electron–hole has been controlled effectively in these composites, which can be seen from their decreased fluorescence emission. The stability results of composites show that they still hold considerable photocatalytic activities after six cycling experiments.

Growth chamber experiments were conducted to determine the effects of UV light and riboflavin on photolysis of 2,4-D applied to Zea mays leaves. Droplets of 100 mg L−114C-2,4-D were applied to Z. mays leaves with and without 10 mg L−13H-riboflavin and exposed to either UV-enhanced or UV-attenuated polychromatic light in a time-course assay. Photolysis of nonabsorbed 14C-2,4-D residues on Z. mays leaves was sensitized by riboflavin regardless of UV light regime, but a larger percentage of nonabsorbed herbicide was degraded under UV-enhanced light compared to UV-attenuated light. Riboflavin was almost completely photolyzed during the first 10 h of exposure; yet, photolysis of 14C-2,4-D surface residues in treatments containing riboflavin increased from 59% at 10 h of exposure to 87% at 42 h of exposure. In corresponding treatments without riboflavin, photolysis of 14C-2,4-D surface residues was 37% at 10 h of exposure and 84% at 42 h of exposure. In contrast, only 7% of the 14C-2,4-D deposited on glass microscope slides was degraded after 42 h of exposure in the absence of riboflavin, whereas 59% was degraded in the presence of riboflavin. Photolysis of 2,4-D on Z. mays leaves in treatments without riboflavin suggests that certain epicuticular component(s) of Z. mays acted as photosensitizers or catalytic agents that promoted photolysis of nonabsorbed 2,4-D residues.

Field experiments were conducted in 1992 and 1993 to determine the timing and amount of rainfall required to activate UCC-C4243 applied preemergence. UCC-C4243 at 0, 70, and 140 g ai ha−1 was applied 1, 7, 14, and 21 d before 0.5 or 2 cm of simulated rainfall. Temporary rainshelters protected field plots from natural rainfall during the 21 d dry period. Herbicide activity was determined in the field by seeding lentil, wheat, common lambsquarters, and field pennycress and in the greenhouse by a sugarbeet bioassay of soil samples (0 to 3 cm depth) taken from all plots immediately before irrigation. UCC-C4243 did not injure wheat; however, lentil population was reduced when simulated rainfall occurred within 7 d after application. Lentil injury was greater with higher herbicide rate and higher water level. UCC-C4243 at 70 and 140 g ha−1 reduced populations of both weed species by 75 and 90%, respectively, when either 0.5 or 2 cm simulated rainfall was received within 1 d after herbicide application. Weed control was reduced with a 21 d delay between herbicide application and water activation. The sugarbeet bioassay showed a linear decrease of herbicide activity over time and also with accumulated photosynthetically active radiation. After 17.9 d, herbicide activity on a dry soil surface decreased 50%. Laboratory investigations show that [14C]-UCC-C4243 on glass slides was photodegraded by near ultraviolet light (290 to 400 nm). Volatilization of 14C-labeled herbicide from glass slides was less than 5% after exposure to turbulent air for 48 h.

Research was conducted to determine foliar absorption of 14C-clethodim and its polar degradation products with five adjuvants and to compare the relative herbicidal activity of clethodim and its polar degradation products. Differential 14C-clethodim and 14C-polar degradation products absorption occurred among the five adjuvants. Adjuvants that mediated rapid foliar absorption of clethodim did not always mediate rapid foliar uptake of polar degradation products. Herbicidal activity of clethodim exceeded activity of polar degradation products regardless of time of day of application or whether adjuvant was used. Inclusion of adjuvant was required for herbicidal activity of polar degradation products. Clethodim activity declined when applied at 0800 h EDT compared to applications at 2000 h EDT. To maximize herbicidal activity of clethodim, adjuvants should be selected that mediate rapid foliar absorption of both clethodim and the polar degradation products of clethodim and that minimize photodegradation of clethodim.

Laboratory experiments were conducted to determine the effect of three phenolic acids, acetone, and riboflavin on aqueous photolysis of chlorimuron and imazaquin. The phenolic acids investigated were caffeic acid (CA), ferulic acid (FA), and p-coumaric acid (PCA). Treatment solutions were contained in quartz vessels and irradiated with 300 to 400 nm UV light in a photoreactor. The extrapolated photolysis half-life of chlorimuron in pure solution was 107 h, compared to a half-life of 0.42 h for pure aqueous imazaquin. Chlorimuron in solutions containing 10 ppmw riboflavin, acetone, CA, FA, or PCA exhibited half-lives of 9, 57, 58, 67, and 146 h, respectively. Imazaquin in solutions containing 10 ppmw riboflavin, acetone, CA, FA, or PCA had half-lives of 0.70, 0.55, 0.55, 0.48, and 0.55 h, respectively. The presence of PCA in aqueous media delayed chlorimuron photolysis, whereas all other compounds, especially riboflavin, sensitized chlorimuron photolysis. In contrast, imazaquin photolysis was delayed in the presence of the test compounds, with riboflavin having the greatest effect and causing in a 68% increase in imazaquin half-life over that of imazaquin alone. Quantum yields for sensitized photolysis of chlorimuron by riboflavin and for riboflavin by imazaquin were 0.1134 and 0.0477, respectively. These results suggest that some soluble and naturally occurring organic compounds may enhance chlorimuron photolysis yet delay imazaquin photolysis in surface waters.

The photolytic degradation of several imidazolinone herbicides in solution and on soil was investigated. Ultraviolet light caused 100% degradation of imazaquin, imazethapyr, and imazapyr, and 87 and 8% degradation of imazamethabenz and atrazine in aqueous solutions, respectively, after 48 h. The order of susceptibility to photolysis in decreasing order was imazaquin = imazethapyr > imazapyr > imazamethabenz > atrazine. In soil Studies, 45% of imazaquin and 52% of imazethapyr dissipated from moist sand after 48 h of exposure. Herbicide dissipation on air-dry sand and on field capacity and air-dry silty clay loam was less than 10% in most instances. Atrazine photolysis was not detected. This research indicates that photolysis of imidazolinone herbicides in solution is rapid. Photolysis on soil occurs readily on coarse-textured wet soils probably due to greater availability of the herbicide for photochemical alteration.

Laboratory experiments were conducted to determine the effects of nonionic surfactants and reaction media (water, glass, and corn leaf residue) on photolysis and subsequent phytotoxicity of chlorimuron and metsulfuron residues. Oxysorbic and octoxynol enhanced rates of chlorimuron and metsulfuron photolysis in aqueous solution and on glass slides compared to controls with no surfactant. Enhanced photolysis of chlorimuron by surfactants was greatest on glass, where 93 and 89% loss occurred after 48 h exposure to ultraviolet light in the presence of oxysorbic and octoxynol, respectively, compared to 38% loss with no surfactant. Similarly, surfactant-enhanced metsulfuron photolysis was greatest on glass with 37 and 67% loss after 48 h exposure in the presence of oxysorbic and octoxynol, respectively, compared to 9% loss with no surfactant. Photolysis of herbicides deposited on corn leaf residue was significantly slower than that on glass or in aqueous media at all exposure times and metsulfuron photolysis on corn residue was enhanced by surfactants only after 144 h exposure. Bioassays confirmed that phytotoxicity of photolyzed herbicide residues was negatively correlated (r=-0.94 for chlorimuron and r=-0.92 for metsulfuron) with loss of parent herbicide as measured by liquid chromatography.

Dissipation of imidazolinone herbicides imazaquin and imazethapyr under no-till field conditions was not affected by straw mulch level (1,300, 3,600, or 5,900 kg/ha) in either of 2 yr of field data. Half-lives averaged 7 d for imazaquin and 8 d for imazethapyr. Chlorimuron half-lives averaged 5 d. Imazaquin and imazethapyr residues did not injure corn (Zea mays) the growing season following application. Injury from chlorimuron to corn planted the next year was greatest where applications were made to the highest straw level, reducing corn yield 6%. In laboratory experiments, uniformly cut wheat (Triticum aestivum) straw placed over sand intercepted all three herbicides equally. Herbicide interception was 16, 43, 69, and 89% for straw levels of 840, 1,680, 3,360, and 6,720 kg/ha, respectively. In the laboratory, simulated rainfall removed more imazaquin and imazethapyr from straw than chlorimuron, and approximately 10% of the applied imazaquin or imazethapyr and 20% of the applied chlorimuron remained on the straw after application of 1.0 cm of water. Imazaquin and imazethapyr dissipated 59 and 20%, respectively, during a 7-d incubation period in the greenhouse. Imazaquin dissipation was equal between sand and straw, whereas imazethapyr dissipation was primarily from sand. Chlorimuron did not dissipate from either straw or sand. This indicated that chlorimuron, a sulfonylurea, was more stable than either imidazolinone under these conditions.

We compared the enhancement of photoactivity of transition metal ion (1 mol% Fe, Cu, Mn, and Zn) doped CeO2 nanocatalysts, and examined the effects of oxygen vacancies and the valence of the doped ions. The nanocatalysts were synthesized using a coprecipitation method and were characterized by x-ray diffraction, scanning electron microscopy, transmission electron microscopy, Brunauer–Emmett–Teller isotherm methods and Raman spectroscopy. The photocatalytic activities of these catalysts were tested using aqueous Rhodamine B (RhB) degradation under UV irradiation. The spherical CeO2 nanocatalysts had a mesoporous structure and ∼15 nm average particle size. The catalytic activity was closely related to the oxygen vacancies and the valence of the doped ions. An increase in oxygen vacancies of doped CeO2 decreased the photocatalytic activity. The photocatalytic activities of the catalysts decreased in the order: 1 mol% Fe > Cu > Mn > Zn > undoped CeO2. The 1 mol% Fe doped CeO2 degraded ∼92.6% of the RhB after 3 h of irradiation, and the degradation obeyed pseudo-first-order kinetics. Liquid chromatography–mass spectrometry indicated that the photodegradation of RhB was a stepwise oxidation process. Under continuous oxidation, over a long reaction time, the RhB was completely oxidized to its final products, such as water and carbon dioxide.

A hindered phenol type radical scavenger (Irganox 1010®) was used to improve the resistance to photo-oxidation in PPV-type polymers. The degradation was performed under blue light (460 nm), and the effect of the added compound was investigated following the intensity variation of absorbance and photoluminescence spectra. The results showed that the addition of the compound brought about a significant enhancement in photodegration resistance without interfering in the electronic properties of the polymers. These results suggest that the free radical scavenger attenuates the decrease of the polymer conjugation length induced by the radiation. FTIR measurements confirm this evidence.