Pigment | EPFL Graph Search

A pigment is a colored substance that is completely or nearly insoluble in water. In contrast, dyes are typically soluble, at least at some stage in their use. Generally dyes are often organic compounds whereas pigments are often inorganic compounds. Pigments of prehistoric and historic value include ochre, charcoal, and lapis lazuli. Economic impact In 2006, around 7.4 million tons of inorganic, organic, and special pigments were marketed worldwide. According to an April 2018 report by Bloomberg Businessweek, the estimated value of the pigment industry globally is

30 billion. The value of titanium dioxide &ndash; used to enhance the white brightness of many products &ndash; was placed at

13.2 billion per year, while the color Ferrari red is valued at $300 million each year. Physical principles Spectroscopy Like all materials, the color of pigments arises because they absorb only certain wavelengths of visible light. The bonding properties of the material

Wastewater and green waste biorefinery Degradation of simple sugars using mixed cultures of purple non-sulfur bacteria: an insight into microbial interactions

Guillaume Crosset-Perrotin

Purple non-sulfur bacteria (PNSB) are phototrophic organisms that have raised interest for both industrial and domestic wastewater treatment and valorization because of their very high assimilation (~1 g CODX g-1 COD substrate) and valuable compounds production (i.e hydrogen, polyhydroxyalkanoates, pigments). PNSB have been studied mostly in pure- or co-cultures with fermentative bacteria. Mixed cultures have been little described. This work aims to enrich a stable association of fermenters and PNSB on a carbohydrate-rich wastewater in a single-step process with a mixed culture. Batches with glucose and acetate at different concentrations were inoculated with an in-house mixed-culture. A chemostat was continuously supplied with glucose (5 g COD L-1) and run at a dilution rate of 0.05 h-1 after start-up under batch mode and baseline stabilization of the PNSB enrichment with acetate. The reactor was constantly illuminated with a light filtered at wavelengths superior to 700 nm. Biomass, pigments expression and substrate depletion were tracked along the experiment. A model was developed to anticipate the biomass growth and the substrates consumption. In the batches fed with acetate, PNSB were dominant in purple biomass (>80% vs. total sequencing read count). The main PNSB population were Rhodopseudomonas and Rhodobacter. With glucose, the biomass turned white. The fermenter Enterobacter dominated the microbiomes (>95% abundance). In the stirred-tank reactor, batch operation with acetate led to the production of a substantial biomass enriched in PNSB (4.0 g VSS L-1) that assimilated the nutrients in a molar C-N-P ratio of 100:9.5:0.1 (- n/n/n). Under chemostat regime with glucose, PNSB were efficiently associated with fermenters in a biomass of 1.0-1.5 g VSS L-1. Phase-contrast microscopy displayed the typical morphotypes of Rhodopseudomonas and the fermenter Clostridium. The glucose was completely depleted. The main fermentation products were acetate (between 3 and 10 mmol L-1), ethanol (between 6 and 9 mmol L-1) and butyrate (between 2 and 4 mmol L-1). The hydrogen yield was low (0.033±0.012 mol H2 mol-1 glucose). A fermenters-PNSB mixed culture was successfully built by microbial community engineering by harnessing the chemostat regime to establish the ecological niches and interactions of these organisms. It provides an excellent opportunity to clean carbohydrate-rich wastewater in a compact single-stage process. In the case of direct application of PNSB, a concentrated biomass can be produced. The biomass can even find interesting applications for resource recovery in the form of, e.g., a protein-rich fertilizing biomass (on food and agricultural aqueous wastes), biogas, bulk chemicals and biopolymers.

2019

Photochemical and photophysical properties of diketopyrrolopyrrole organic pigments

Various aspects of the pigment class based on 1,4-diketo-3,6-diphenyl-pyrrolo(3,4-c)pyrrole (DPP) are investigated. The thesis consists of two parts: the first part, motivated by the degradation problems of DPP, focuses on the molecular photophysics of the DPP class of compounds. The second part, motivated by photovoltaic applications, focuses on the electrical and photovoltaic properties of solid state DPP. Investigation of the photoluminescence of the main commercial derivative, p-Cl DPP (PCD) showed, that the emission of the pigment in polymer matrices may be attributed to aggregates at the surface and that it is sensitized by monomers of DPP. From the distinct excitation spectrum of the monomers it is thus concluded that these play a major role in the photoactivity and photodegradation of the pigments. In solution the dominant role of singlet oxygen in the degradation of the molecule has been shown. The quenching of the singlet excited state of DPP by oxygen efficiently produces singlet oxygen and triplet States of DPP. The latter is again an efficient sensitizer of singlet oxygen. The triplet state energy has been measured for DPP (28.5±2 kcal/mol) and the p-dimethylamino derivative DMADPP (29.5±2 kcal/mol). The triplet energy for DMADPP is slightly higher than for DPP, although the respective singlet energies have the opposite trend (DPP: 56 kcal/mol and DMADPP: 51 kcal/mol). Based on molecular orbital calculations this observation is attributed to the structure of the HOMO and LUMO orbitals and it is concluded that the large singlet to triplet energy splitting is a property of the core of the pyrrolopyrrole chromophore. DPP and DTPP (dithioketo-DPP) are used in electrochemical and heterojunction solid state photovoltaic cells based on porous TiO2 electrodes. MCDPP, a derivative of DPP using a carboxylic anchoring group yielded an incident photon to current conversion efficiency of 47% in a photoelectrochemical cell. The solid state photovoltaic cells yielded poor photocurrents. The use of MCDPP in the TiO2/DPP heterojunction increased the photocurrent. Surface photovoltage spectroscopy and Kelvin probe measurements were used to determine the workfunction of DPP (5.38 eV), DTPP (4.95 eV) and DMADPP (5.08 eV) and to investigate surface and interface band bendings of DTPP on SnO2. A band diagram is proposed for this system. DTPP and DPP showed both p-type band bending.

EPFL1997

A General Framework for Pearlescent Materials

Ibon Guillen Serrano, Wenzel Alban Jakob

The unique and visually mesmerizing appearance of pearlescent materials has made them an indispensable ingredient in a diverse array of applications including packaging, ceramics, printing, and cosmetics. In contrast to their natural counterparts, such synthetic examples of pearlescence are created by dispersing microscopic interference pigments within a dielectric resin. The resulting space of materials comprises an enormous range of different phenomena ranging from smooth lustrous appearance reminiscent of pearl to highly directional metallic gloss, along with a gradual change in color that depends on the angle of observation and illumination. All of these properties arise due to a complex optical process involving multiple scattering from platelets characterized by wave-optical interference. This article introduces a flexible model for simulating the optics of such pearlescent 3D microstructures. Following a thorough review of the properties of currently used pigments and manufacturing-related effects that influence pearlescence, we propose a new model which expands the range of appearance that can be represented, and closely reproduces the behavior of measured materials, as we show in our comparisons. Using our model, we conduct a systematic study of the parameter space and its relationship to different aspects of pearlescent appearance. We observe that several previously ignored parameters have a substantial impact on the material's optical behavior, including the multi-layered nature of modern interference pigments, correlations in the orientation of pigment particles, and variability in their properties (e.g. thickness). The utility of a general model for pearlescence extends far beyond computer graphics: inverse and differentiable approaches to rendering are increasingly used to disentangle the physics of scattering from real-world observations. Our approach could inform such reconstructions to enable the predictive design of tailored pearlescent materials.

ASSOC COMPUTING MACHINERY2020