Method of evaluating pH using a metallic nanoparticle incorporated nanocomposite-based optical pH sensor
Inventors
Ohodnicki, JR., Paul R. • Wang, Congjun • Brown, Thomas D. • Kutchko, Barbara
Assignees
Publication Number
US-11408827-B1
Publication Date
2022-08-09
Expiration Date
2035-04-24
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Abstract
A method for evaluating the pH of an aqueous solution by utilizing the optical properties of a pH sensing material comprised of plurality of optically active nanoparticles dispersed in matrix material. The optically active nanoparticles have an electronic conductivity greater than about 10−1 S/cm and generally have an average nanoparticle diameter of less that about 500 nanometers, and the matrix material is a material which experiences a change in surface charge density over a pH range from 2.0 to 12.0 of at least 1%. The method comprises contacting the pH sensing material and the aqueous solution, illuminating the pH sensing material, and monitoring an optical signal generated through comparison of incident light and exiting light to determine the optical transmission, absorption, reflection, and/or scattering of the pH sensitive material. The optical signal of the pH sensitive material varies in response to the pH of the aqueous solution.
Core Innovation
The invention provides a method for evaluating the pH of an aqueous solution by utilizing the optical properties of a pH sensing material comprised of a plurality of optically active nanoparticles dispersed in a matrix material. The optically active nanoparticles have an electronic conductivity greater than about 10−1 S/cm, with an average diameter of less than about 500 nanometers, and the matrix material experiences a change in surface charge density over a pH range from 2.0 to 12.0 of at least 1%. The method involves contacting the pH sensing material with the aqueous solution, illuminating the sensing material, and monitoring an optical signal generated by comparing incident light and exiting light, which varies according to the pH of the solution.
The problem being addressed concerns the difficulty in measuring pH accurately in harsh environments such as downhole and underwater conditions where high temperatures, pressures, chemically corrosive species, and high salinity exist. Conventional pH sensing technologies fail due to instability of electrical and electronic components and the limitations of organic dyes and indicators under these conditions. The invention seeks to provide an optical-based pH sensing approach exhibiting strong, reversible, rapid responses that are stable at elevated temperatures and pressures without the need for electrical connections or protonation/deprotonation mechanisms that limit sensor durability and deployment.
The core innovation lies in exploiting the optical property changes of thin films containing optically active metals or metal oxides in a matrix stable under harsh conditions. Unlike prior art relying on organic dyes or swelling polymer matrices, this method uses conductive nanoparticles such as noble metals (Au, Pd, Ag, etc.) dispersed in inert matrices like silica that undergo changes in surface charge density with pH, enabling measurable optical responses via absorption, transmission, reflection, or scattering. Calcination of the sensing materials at elevated temperatures further enhances stability and suitability for downhole applications. The approach allows for non-invasive, optical interrogation, including via fiber optics, enabling real-time spatial mapping of pH in hostile environments.
Claims Coverage
The patent includes two independent claims, detailing methods for evaluating pH using a calcined pH sensing material with specific nanoparticle and matrix characteristics, and for monitoring the optical signal to evaluate pH.
Method of evaluating pH using a calcined pH sensing material
The method uses a pH sensing material calcined at at least 150° C., comprising a matrix material with volumetric change ≤1% over pH 2–12 and optically active nanoparticles with electronic conductivity >10−1 S/cm, absorption cross-section ≥10−16 cm2, carrier concentration ≥1017/cm3, bandgap ≥2 eV, and average diameter <500 nm. The method includes illuminating the material with incident light, collecting exiting light, and monitoring an optical signal comparing the two via optical spectroscopy to evaluate pH.
Smaller nanoparticle size for enhanced sensing
The method specifies that the average nanoparticle diameter can be less than about 100 nanometers to optimize optical response.
Use of metallic nanoparticles for optical activity
The optically active nanoparticles can comprise metals, specifically noble or precious metals such as gold, palladium, silver, platinum, ruthenium, rhodium, osmium, iridium, or their combinations.
Matrix material composition
The matrix material of the sensing material can comprise silica.
High temperature operation and calcination
The method extends to using pH sensing material calcined at temperatures of at least 400° C. for aqueous solutions at or above 400° C., thereby supporting high temperature pH monitoring.
Optical interrogation with interrogator and meter
The method comprises using an interrogator optically connected to the pH sensing material to emit incident light, collect exiting light, monitor optical signals, generate measurements, and communicate with a meter to display the pH reading.
Monitoring shifts in optical signal
Monitoring involves detecting shifts in the optical signal over time to indicate changes in pH based on variation in transmission, reflection, or absorption.
The independent claims cover a method for pH evaluation using a calcined nanoparticle-based pH sensing material with defined nanoparticle characteristics, matrix volumetric stability, optical interrogation steps, and applicability to high-temperature aqueous solutions. The claims highlight nanoparticle size, metallic composition, matrix makeup, and system components for measurement and display as main inventive features.
Stated Advantages
Eliminates the need for electrical components and connections at the sensing site, reducing failure modes in harsh environments.
Provides strong optical response with reversible interactions allowing rapid and stable pH sensing.
Enables pH sensing at elevated temperatures and pressures, applicable to downhole and other harsh environments.
Utilizes stable inorganic nanoparticles and matrix materials improving chemical and temperature stability compared to organic dyes.
Compatible with optical fiber interrogation allowing real-time spatial pH mapping and distributed sensing without bent fibers.
Documented Applications
Monitoring chemical composition in harsh environments including downhole and underwater conditions for fossil energy applications such as unconventional, deep, and ultra-deep oil and gas recovery.
Environmental monitoring in reservoirs for CO2 sequestration.
Accurate pH measurement downhole at reservoir temperatures and pressures to predict corrosion and scale potential.
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